You're enchanting the FREAKIN covenant. Ensuring peons do not leave is child's play, assuming you have decent Mentem. Now EVERYONE acts in accordance to my whims. Or Hubris, which amounts to the same thing. BWAHAHAHA!
On the other hand, if you have indecent Mentem, [strike]everybody will be too busy staring at its breasts to obey you[/strike] you can still probably ReCo to prevent jumping and leaving. But then you have to get into the semantic metaphysics to figure out if the old grog croaking counts as breaking it or if his corpse is him enough to count as long as nobody picks it up.
Ah, no, obviously not. Again, by the rules, I get to choose the elements which make up the Item. I am aware of only one way to enchant Animate matter, and it is lost to the Order, so people, of course, will not be part of the enchantment, anymore then the Air of the lab is when I enchant a staff. Come on, guys, you're reaching.....
(And the the Arena, again, read the example. "The Structure" is not enchanted at all, the soil is. The structure only serves as the boundary, but is not enchanted. (Which would be stupid, yes? You don't want to work your audience into a frenzy......) Mind, that example opens up real questions. I assume, in canon, the creation of the Arena, and it's enchanted field, did not create riots all over Rome as the soft dirt was tracked other places. So, either the "Dirt" was enchanted, but there's an amount that can be taken from the area before the Enchantment is lost. How much? Or, the area of the boundary has been enchanted, and "dirt" can be brought in, and taken out, at will. Sounds like a real promising place to get a Breakthrough on Auras........)
I've always found that example to be a bit henky.
Serious question as to how one handles removing dirt and how/when it affects the enchantment. YSMV.
I'm open to the idea that you can use Boundary to enchant the soil - but that will still not give you enchanted building, just enchated soil.
That aside, there's still this:
and
thus device effects cannot use T: Boundary. The explicit exception to this rule is Hermetic Architecture (ref TMRE, p. 98, thrid bulletpoint from the top, under Investing the Effects), making this possible via a (mystery) Virtue which is assumed (indeed demonstrated) in the example in the box, TMRE, p. 99.
It is interesting to note that an enclosed arena could have been enchanted using T: Room, with sufficient modifiers for size, as it fulfills the definition of a Room (ArM5, p. 113).
EDIT:
PS: While a group of Boundary cannot be used as an enchanted device without certain virtue, single Structures certainly can. I have been known to argue that en enchanted lab/tower is possibly the best way to use the Talisman rules, for non-combat magi.
PPS: If you do not have the Hermetic Architecture Virtue, why enchant the whole building anyway? Especially as you arguably don't get your Verditius discount, as you're not creating the item (tower/building) for the enchantement, but enchanting something which already exists (ArM5, p. 93).
Instead, just create something smaller and more managable - a golden brick perhaps - and brick it into the wall. cheaper, easier, more extendable (as you can make more golden bricks) and you don't have to mess with the whole outdoors lab. Just use R: Touch and T: Structure.
We can argue about the rest of it all day to no point. As to your PPS, two reasons. First, because it wasn't important. The point (That EVERYONE overlooked) was "What happens when two permanent enchantments overlap. If the gold brick makes you feel better, use it. Again, what does it do about the Lab in the structure that has already been enchanted?
And if I were to do such a thing in game, why would I use a gold brick? Single point of failure, easy to steal, and lots of reasons for people to want to steal. You don't think Verditius are aware of theft, and think it's a big problem? Heck, Verditius see theft where there isn't any! (See Item Attunement, Ars Magica, Houses of Hermes, Mystery Cults). Well, good luck stealing my Covenant!
... But the air isn't part of the staff. From a metaphysical standpoint, the residents are no less part of the covenant than the buildings, so if you're enchanting the covenant, you'll need to include all those factors. Now, granted, you could choose to enchant your covenant with the highest individual part (probably your biggest or rarest-material building) rather than the whole, in which case the disconnect wouldn't break effects not tied to the s/m bonuses, but then things start to get kind of... Weird.
To directly answer the OP, it really depends on HOW you are enchanting the covenant. I don't know how hermetic architecture works, but I doubt you can use your existing "standard" lab for it, therefore you need to meet the hermetic architecture requirements. If you actually build a lab large enough to surround whatever part of the covenant you wish to enchant (such as a single large structure), then you need to build a new lab that meets THAT requirement.
Unless HA allows use of your already existing lab, I would vote for no overlap, and you end up with (and must support) two labs.
I'm not sure I follow.
I thought the problem was that part of the (covenant/building/whatever) you're trying to enchant, has already been opened (for enchantment) and enchanted. To which I repeat:
If your problem is that two (or more) enchantments are affecting the same target, I believe we've all ignored it because there's no problem. A single object/individual can be the target of any number of effects at the same time. Or am I still not understanding the point?
Actually, using a golden brick is not that hot an idea, if you can enchant the effects you want in a single season each. Then just invest each effect in a seperate stone, and then brick them up.
The golden brick is merely suggested because it has about the same Vis capacity as a fair-sized stone tower.
The heart of it, I think is the interaction between two "wholes". As you have done, a "Room" can be enchanted. It is a whole. A structure can be enchanted. It is a whole. But a structure can have many rooms. Perhaps if I change the scale. I have enchanted a gem (And only the gem) which is part of a staff. The Gem is whole, by itself. Now, if I enchant the Staff to be my Talisman, do I get to include the gem's enchantments? The Spaces of the gem? The form and effect bonuses? Does the gem get the Magic Resistance of the Staff? I started with my example because I would want, as a Verditius, to enchant my lab. Then my thoughts got large......
If you enchanted a gem, the gem is the enchanted item. It could be attached to the staff, but it wouldn't receive the shape and material bonuses of the staff unless it was part of the staff at opening. A staff to which the gem with invested effects is attached can't be attuned as a talisman unless it has been at least prepared for enchantment on its own. And when you attune said staff, it's just the staff, not the gem. IF you attune the staff, the gem doesn't get any MR. IF you attune the Gem it doesn't provide its benefits of MR to the staff, nor does it allow you to unlock the S&M bonuses associated with the staff and the wood species. IIRC, Great Talisman allows incorporating additional components into one's talisman at a later time.
What you are saying, from what I am reading, If I enchanted the Covenant, the previously enchanted lab would not be included. Excellent. What I wanted to hear, but I needed/wanted independent confirmation. If I ever get a chance to do this, I don't want to get tripped up by the Code on Spying.......
I'm not exactly sure what you're asking.
Tellus also effectively shut down the idea of enchanting T:Boundary effects into the device. And if you use dirt as your guideline for the amount of space, destroying some portion of that dirt, or even moving it might render the enchantment inert.
It would, perhaps, be best to fully spell out your plans than try and get is to come to an agreement about what you want to do and take what we say as an endorsement of that, when we really aren't endorsing your specific action, but the analogies, and snippets that you provide. I don't think you can do what you want to do the way you want to do it. I think it's already been pointed out that you have a massive upkeep problem for the seasons during which such a large lab is operable And yes, everything in the covenant must be within the lab, so it is large, and it would have a lot of emptiness, because that emptiness of the lab is about it being empty of hermetic/mystical energies that are synchronous to your actual lab space.
Now you bring up code violations of possible scrying. So, where are you going with this, and what are you planning to do?
Tellus? Not really. Ya'll brought up "Boundary", not me. I pointed out that it is on the Extended Shape and Material chart, which is a sidebar, completely seperate from Hermetic Architecture. Structure *10 or *100 is fine with me. Certainly easy enough to make all the structures one if it comes to that. As to the dirt, I think not. "Roads" is a formal,canon, guideline for Fairie Magic, yes? Core book, yes? Pretty sure if that was an issue it would have come up by now.
Plans? I have no plans. I, alas, am not in a game. I was just geeking The Mysteries, and the Extended Shape and Material chart inspired me. A flying Castle/Covenant? Gosh, what fun! But starting fresh, leaving behind all that history? Not so cool. So, as I asked, what would be the interaction between old and new enchantment? You guys couldn't get past the lab thing, but changing the language got me the answers I was looking for. So it goes.....
Sure, we brought it up (context of Huge size that you brought up), and then you pointed to an effect in TMRE that used it. Tellus then pointed out that particular effect was T:Boundary, and that it wasn't within the capabilities of normal Hermetic magic, only HErmetic Architecture.
What does Faerie magic Road (Range) have to do with dirt? I certainly wouldn't attempt to enchant a road, but something that works at Range:Road. You are mixing effects, items and ranges into one huge amalgamation of stuff. So, if one were to destroy the dirt in the road, would that affect the Range of Road is completely different if a road were enchanted and part of it being destroyed...
Not sure you got any answers, except the ones you wanted to get out of it. Enchanting a covenant is completely different from designing effects that cover an entire covenant. If one destroys dirt inside the covenant, the covenant can still be affected by any mystical effect that would target the covenant. If the dirt of the covenant were invested as a magical device on some huge lab that surrounds the covenant (this is important) it's now considered an item. IF someone destroys some of that dirt, it's a very real problem that you would have to deal with. Consider the example of your staff, if someone destroys part of the staff, the device is broken, same situation as destroying any of the dirt invested as a magical device...
I'd personally disagree with that interpretation.
My opinion:
You can only enchant whole things. You can't enchant "this staff but not the gem on the top"; but you could enchant "this staff that has a fitting for a gem". You'd have to separate the objects to do so.
You'd somehow need to define a whole object that is the Covenant, but doesn't include that lab. There are ways to do this (temporarily move the lab somewhere else for instance) but it's not a trivial task.
At risk of sounding imperialist, your opinion is wrong. 
You can, in fact, enchant a compound item while opening only one part. This lets you get the Shape bonuses for the other attachments, but if they're ever separated, any enchantment that benefited from outside Shape bonuses is lost.
Granted, this only goes two ways: Enchant everything, or enchant the most expensive part. You can't "enchant everything except one part" unless your thing has only two parts, which is multiple orders of magnitude lower than all the parts of an entire covenant.
Where do you find this?
If a magic item is "whole" removing any portion of it should render the entire item useless, no? Especially considering that the part, say a gem might contain the vast majority of the vis for a compound item...
If your already spending the Vis just build a whole new covenant with Verditus runes. As was mentioned in another thread you can create impossible things with your outer mystery. You apparently can build anything in ones season if you simultaneosly open it for enchantment. If you have the RAW materials.
So go wild. Turn an orchard into a grove of living houses with seamless walls of woven branches. Excavate tunnels and turn the sand, stone, and clay into glass walkways, stone pillars and cearmic tiles and piping. You
I refer to the rules on enchanting part of an item, page 97 of the core rulebook. Third paragraph of "Preparation for Enchantment." I suppose my use of the phrase "compound item" was inaccurate from a rules perspective, for which I apologize