What spells do you guys actually use for protecting yourself or your items? What kinds of things do you put on the door to make sure people who ignore your sanctum marker and can get past any mundane locks can't trash your lab and won't come back? (Includes enchantments, not just regular spells) What kinds of defensive spells or enchantments do you like to put on your own apparel before you leave the safety of the covenant in case your shield grogs fail at their jobs? What spells do you put on Watching Wards on your enchanted items to laugh at all those losers who try to investigate them (possibly after you die)? Any of your favorite things in that rather general category of "(passively?) protecting yourself and your stuff."
I like to vary things based on the character. I had a magus who had a minor magical focus of oak. His covenant was surrounded by a ring of oak trees upon which all sorts of circle spells were cast. He had wooden armor (made supernaturally hard) and a tree that acted as a guard.
I like Ranulf from Magi of Hermes (disclosure, I wrote that chapter so I naturally wrote what I was fond of). One of his themes was doing everything as an ignem spell regardless of the availability of non-ignem ways to accomplish his goals. His talisman detected arrows (shriek of the impending shaft) and incinerated them (a linked trigger creo ignem effect). He has a spell that engulfed him in fire to convince others not to attack him lest they burn their attacking limbs off.
My biggest problem with using spells or enchantments to protect my items or favored locations is simply how weak magi are outside their specialties. Unless my character is specifically focused on protection spells (and I've never made such a character) then they won't be very good at making protection spells, as a rule. I mean, I've made Rego specialists, and most good defensive spells involve repelling things, which Rego does well. But any skill-level-appropriate challenge by my SG's definition of the term will not be deterred by a spell unless I've got both the Technique and Form going into said spell full-force, and the wards against things like fire and scrying are rather high-level by necessity, meaning that any non-Rego specialist just has no chance of pulling them off with a useful amount of Penetration.
So, in short, I haven't developed very many passive protection spells. Mostly, I'll use Waiting Spell with a vis-boosted spell set to go off, with another spell on the item to protect it from the element I'm using. Ward Against Flames and Ball of Abysmal Flame have been a nice combination for my Ignem specialists. I'll just hope that whoever is stupid enough to trigger my item proceeds to die from it, and call it a day, rather than putting shells and tricky illusions and wards against physical touches and whatnot; it's really expensive to make those last for a significant amount of time without Ring duration, at any rate.