When I lived in Montana I had rats in my barn that were as big as a small dog. They were too smart to be caught in a standard "pedal" snap trap... they just flipped them over and took the food. They were also too smart to allow me to shoot them; whenever I came into the barn with a gun, they would be absolutely silent. The one trap that worked flawlessly was as follows: take a 5 gallon plastic bucket with a lid that closes tight (like a paint pail). Cut a hole about 3"-4" in diameter in the lid. Place two #0 leg traps (the smallest you can buy), in the bottom of the bucket. Make sure to attach the trap chains to the handle of the pail or the rat will just run off with the trap. Place half an onion (because they smell and attract the rats) in the bottom of the bucket in between the traps. (I also added peanut butter in case the rats didn't like onions.) Finally, make sure the bucket itself can't be hauled off by a large rat. (I set it inside an old car tire.) The rat crawls down through the hole and, because the traps take up all of the floor space in the bottom of the bucket, they can't step anywhere without getting at least one leg caught. Each time I caught a rat, I found it the next morning sitting on top of the bucket with one leg in a trap, but unable to get away because the trap's chain was attached to the bucket handle. (You then need to be ready to shoot the rat, or dispatch it some other way.)
