If you load a shotgun with a round designed to not penetrate a wall, why do you think this same round will penetrate a person to sufficient depth to cause incapacitation. #8 shot causes a nasty shallow wound. It is made for little birdies, not people. Would you take a .22 on a deer #8 Probably hurts alot but it does not reach the vitals. If that is the reasoning behind your round selection, then you need to think some more. If you want at shotgun because of it's KNOCK DOWN POWER, then you need a round that will do the job. 00 buck might be a good choice here. Sure it will penetrate a wall but if you shoot the BG and not spray rounds towards your childrens rooms...... Sigh, End rant.
Home defense gun..... For me, depends what I have out of the safe at the moment. I don't ever expect a single round of ANY caliber to stop anyone. I shoot until the threat is down or stops being a threat. My Home defense shotgun is also my onduty gun. Benelli M1 Super 90 with Surefire weapons light and a side saddle. My side saddle is full of slugs and the tube is full of 00 buck. For home defense the side saddle is just about worthless. I also have an AR but prefer the Shotty for home defense. If I just knew something bad was going to happen, the 12ga is what I would reach for. And I would still apply the shoot until the threat is down method. If you want to search your home for BG's rather than hold up and call the po po, then a pistol is less likely to be grabbed away from you than the protruding barrel of an 18" or (Dear God) 26" Shotgun. A shotgun is a stand off, defensive weapon. Great for covering a door with your family behind you and your wife on 9-1-1. But using a Shotgun to go prowl around the corners of your home is asking for trouble. I DO believe that racking a round into a shotgun will scare away MOST would be BG's. But never count on anything. Who knows what some crack head is going to do. Ultimately, I think, Training and mind set are more important than the particular weapon used.