From the Spider's Spellbinding Compendium: Hiding and protecting your web
Now that the basics are covered,one need to think about magical robbers.
- Supernatural Intruders
In a way, these are simple to deal with: a simple Webbing with a Perdo Vim enchantment should give them pause.
What may be problematic is when such being can just enter the protected area though an unforeseen direction, usually to serve as recon for a Mage.
To protect against that, it's probably easier to just have circular rooms protected by Webbings, although, in some cases, wards may be more effective.
Maybe combine an outward repulsive protection with inner destructive traps, or a magical prison, which lets a spirit enter, but not leave? This achieves a similar effect, while leaving you with a prisonner to interrogate. Sadly, this will only work against the weaker entities.
An intriguing possibility would be a circular trap that enslaves any supernatural being within its bounds. Not only would this be more efficient than a prison ward, it would turn intruders into allies. While this is also possible with mundanes, captured supernatural creatures make eternal guardians, while enthralled mundanes will soon die of hunger or thirst.
Note that a clever magus might use similar techniques, which leads us to...
- Omnidirectional Intruders
Burrowing through the ground, flying or who knows what else, are all viable means for a smart and ressourceful intruder to enter the defended zone. Never assume your thief or assassin will gently go through the maze you've patiently designed.
How can we deal with this?
The easiest is the one I've taken with my own sanctum and laboratory: hide the protected area, access it through translocative magics.
There might be useful regios, too, but yu can't count on this. If you're lucky to find a single entry regio to use for your purposes, good for you. Nonetheless, unless you're sure it is exceptional enough not to be accessible through Second Sight or Piercing the Veil spell, I'd just discount this.
Which leaves us with the hardest, but more effective, technique: The omnidirectional maze. In a nutshell, you must first create your whole protected area while keeping these precepts in mind, building it like an egg, with circular layers of defenses taking care of the problems with adressed before.
Personal Notes
Obviously, this last solution requires a lot of place and planning, but maybe I'll be able to use it one day if I get to build that fallback bunker I dream about. As far as I know, it is untested to this day, but I strongly believe it to be potentially more effective than the other two techniques. Nonetheless, as always, redundancy is the way to go