The 12 ga is just fine for close work. A gas operated semi auto would be the best choice. I always say gas operated since you can cycle it with one hand, off-hand, with no need to brace it on your shoulder. Sometimes you need the other hand for stuff. Shorter barrels are good where defense is the issue. Extended mags so you can load six or more rounds are good. OO Buck should be your first choice and if you thot you’d get off more than three shots then a bandolier is best for keeping the mag topped off.
And try to keep it out of the lake. You’ll need it before you want to lose it. A few more no-knock raids and you’ll know it’s time. Fill those cinder blocks with something dense.