I do this for a living (great job, btw) and while i agree that snap traps are the best, peanut butter can be licked off the trigger, as noted. Most traps have a small anvil to hold bait in place. Rats love dried fruit, raisins, cranberries, etc. Put one under the anvil and bend it down to secure the fruit. Bacon works too, i'm told, but I've never had any left over...