I'd suggest a .22-250. Load it with a 50gr varmint bullet and they won't go back into the hole unless they just happen to land there. I shot a nice fat groundhog with my 22-250 and a 50gr Nosler Ballistic Tip right at 200 yards. Hit it in the chest, and it turned his chest and abdomen completely inside out. It was gruesome, but very effective. He didn't do anything but roll down the hill he was standing on when he died.

Mike