This is what I am using:Peep, look into Ramik. I got it at TSC. It isn't a poison but an anticoagulant. The rats eat it and die but any animal that eats them is not harmed. That said I've never seen a dead one just their absence. Doesn't take but a couple of 'pills' placed where other animals won't get to them.
I did find a dead rat yesterday. The others should be dead in the nest.