good luck trying to stop some breeds, especially jack russells.
My ACD has managed to kill a couple of foxes, hasn't affected her at all. As far as the rats welfare, i view things like foxes, Rats, rabbits etc as feral pests that do so much damage to our country (comes from my farming background i guess).
They still need to be killed quickly though, and a dog will kill them quicker than what poison will.
I don't think it's in-humane, especially given the diseases feral rats spread. you don't want them crawling all through your pantry at night! there's probably plenty of people that won't agree though.
"He is your friend, your partner, your defender, your dog. You are his life, his love, his leader. He will be yours, faithful and true, to the last beat of his heart. You owe it to him to be worthy of such devotion" Author Unknown