Catching a rat is not always as simple as setting a trap with a small hunk of cheese. Rats are survivors by nature, and can be skilled at avoiding traps. Use the following, proven method to finally catch a stubborn rat, often without killing or harming the creature.
Let the rat win for a while. A smart rat often can beat a spring-loaded trap, stealing the bait without tripping the bar. Allow this to continue for a couple of days. If the rat does not seem interested in your bait, try something else. Peanut butter often works, because rats will linger as they eat it.
Put the spring-loaded trap on top of a glue trap. Position the spring-loaded trap on the glue mat so the rat can not get the bait from any angle without stepping on the adhesive. Make sure you bait the spring-loaded trap with something you know the rat likes.
Catch your rat. The spring-loaded trap may not catch the rat, but the glue likely will. If the rat sniffs or tries to sample the bait, he will be caught.
Check the trap regularly. The last thing you want is the rat dying a slow, agonising death. People often ignore traps, allowing rats to die of starvation. If you check the trap daily, you may find the rat alive. Often, you can deactivate the adhesive on the glue trap with vegetable oil or another solvent, which could allow to you free and relocate the rat.