I think it's completely normal. Dogs are carnivores! I don't know exactly how safe it is to eat a wild gopher, because I have no clue what parasites or diseases, if any, could be passed on to your dog. I'd call your vet and ask if there's any health concerns with gophers. But, as far as your dog eating a small animal, that's just nature. If you talk to your vet, though, please post what he/she tells you, I'm curious!