Get yourself a cheap, well made 12GA shotgun. It's one of the most practical home defense guns, it's easy to handle, doesn't require a whole lot of skill or practice to deploy and generally scares the shit out of people. Also, your Weimaraner was bred as a gun dog, he'll think it's cool.
A Mossberg Maverick Model 88 Security (12GA) with an 18.5" smooth barrel will run you right at $190 - $210. This is the typical "cop" shotgun. Also Maverick 88 barrels are compatible with Mossberg 500 model barrels within gauge and capacity... This gives you a lot of options, accessories and spare parts to work with if you decide you want to do more with it later. Buy a couple of boxes of Federal 12 GA Low Recoil Tactical 00 Buckshot. The 88 will handle 3" magnums but skip it. That macho bullshit beats the hell out of your shoulder. If 2 3/4" 00 Buck won't do the job, you should have brought a machine gun...
But seriously, get an 88 - You'll like it, it will be cheap, easy to shoot, it's well made and they do well even if mistreated and are never cleaned.
Just jacking a round into the chamber on these has been known to send bad guy running the other way. It's an ominous sound. Not to mention it will clear a hallway in a heartbeat and will make hamburger out of anyone who earns the business end of it.