The most effective rat trap I've heard of is the old school long spring trap......size 1 1/2. You can find them used on ebay for about $5 each. Set against a wall where they are using for a run. They hop on the pan, trap snaps shut and crushes them between trap's jaws. Some will cover the trap with a light rag.....like a shop rag......so they just see it as an object to step on......no bait is used at all.