Defenses? It depends very heavily upon the wizard. Obviously, there are many different levels of defenses, both active and passive and their usability will depend upon the desires of the wizard. Guards and Wards? It's great if you don't mind walking through fog to get to the restroom, tearing through webs to get downstairs for breakfast, and casting gust of wind to get rid of the stinking cloud in your entryway when you want to go outside. However, if you prefer a few more comforts, you probably won't be using guards and wards while you're at home.
So, what are the basics. A lot of detect spells are blocked by lead or gold so you're probably going to have a lot of one or the other. Gold for classy and ostentatious wizards, and lead for wizards with darker or more spartan tastes. Those who prefer security without ostentation may opt for lead and then paint it. A thin sheet of gold or lead works so you're probably talking gold or lead leaf in any event.
If your campaign world allows people to stop teleportation, etc with things like gorgon's blood mixed into the mortar of a castle, odds are good that wizards will generally do such things. Arcane lock is cheap (no more expensive than a regular lock and a good deal cheaper than a good one) and permanent, so it will probably see extensive use. If the wizard employs servants who need to use doors, it is likely that there may be a password for the arcane locks in the common areas.
Alarm is also likely to be a common spell for protecting areas that are not in common use, and mordenkeinen's private sanctum and dimensional lock are also quite likely.
The use of things like sepia snake sigils, explosive runes, magic mouths, etc will most likely depend upon the number and nature of the wizards' servants as well as the wizard's attitude. The kind of wizard who casts guards and wards while he's at home would have everything warded, the kind of wizard who prefers servants and luxury would use a bit more restraint.
Active defenses would likewise reflect the style of the wizard who created them. One kind of wizard will go for golems and shield guardians. Another kind will go for undead. Yet another kind will go for summoned demons or devils, and still others will go for bound elementals. Still another kind of wizard would use dominated or charmed monsters. Invisible Stalkers might be a possibility for the kind of wizard who keeps human guards for show but has mysteriously effective defenses anyway.
Also in the section of active defenses, you might want to consider amenities. Unseen servants are mentioned above, but what about dominated dignitaries and/or enemies serving as scullery maids because it amuses the enchanter to see his proud enemies doing humiliating tasks. If they have other abilities, they can also figure into active defenses. (The guy with the mop was once the best swordsman in the land but he insulted the wizard and now rather than advising and championing the king of a distant land, he scrubs floors in the wizard's tower... oh, and he is also commanded to attack intruders--should he see any). Summoned lillends could provide music--or a defender. A cruel wizard with a taste for gladiatorial matches might have a menagerie of dangerous beasts that he pits against each other for his pleasure--and that can be released upon intruders. A perverse wizard might keep a succubus or an erynies in his bedchamber. The possibilities are endless.
However, the essential thing is going to be this: consider the personality and character of the wizard. One wizard might have an imposing windowless tower of granite in the wilderness. Another might have an ostentatious and luxurious manor in a city. Yet another might live in a humble farmhouse... with an interior that belies its humble exterior. Another mage might well live a double life--ordinary, if eccentric, merchant to the outside world, but with a secret lair under his manor where he does his wizardry rather like the bat cave. A final kind of wizard might live in an actual hovel--some kind of run-down building filled with trinkets, odds and ends like the woman in the new Pirates of the Carribean movie. (If she needed defenses, a shield guardian standing in the corner like a clothes horse would not have been out of place).
The important thing is not just that defenses be effective; it is also essential that they be in keeping with the character of the wizard who uses them.