Originally Posted by Doug M.

Layers, darn it, LAYERS.

Fence w/locked gates, outside lights, locked doors, dogs (preferably larger breeds - in part because the bark is more attention getting, and if you have two or more of them, an intruder who gets past the other stuff will have their hands full). Discourage with target hardening - if a potential offender goes elsewhere, you have prevailed!

Guns: someone who is proficient with a K frame full of 158 grain SWC is a lot better off than someone who is a clod with an AR or shotgun. I prefer the AR for better ballistics, less risk of penetrating walls, red dot sight, mounted flashlight; easier to shoot. The ballistics research is clear on shotguns - birdshot is clownshoes. #1 buck has been shown to be the best in terms of damage (more crush area than 00 or #4, better penetration than #4). I have mine loaded with slugs because a) my academy taught them as default, and b), my shotgun is also set up with a red dot and integral light. My additional rounds are 000 - because I bought a lot when that was the best thing going. I also have a couple of pistols.

I have considered a 9mm carbine for a couple of reasons now. One os that there are a couple of places making 9mm ARs that actually work, and are designed around the 9mm pistol mags instead of using adapters. The ammo is cheaper and one can shoot it in places that will prohibit 5.56X45. 9mm +P out of that will be at or above .357 magnum levels, even if I were to go with an SBR/can combo. Drawback, of course, is that these rifles cost as much as a service worthy AR ($2K- ish), and so the ammo flexibility has to be worth it in order to justify the money for an additional rifle.

Over penetration is less of a real concern than it is portrayed to be if one tracks down the valid research (such as by Doc Roberts). The first step to reducing the risk is to HIT THE TARGET; proper ammo might come out the back, but often with enough less energy that the risk of further penetration is reduced. A MISS carries a lot more risk to others (and your own exposure) than any purported risk from "over-penetration".