Rats can squeeze through holes the size of a quarter. That’s smaller than you think. Seal up the gaps—around pipes, behind the fridge, under the sink. Use steel wool packed with caulk. Why steel wool? Because rats can’t chew through it. They’ll try, though. Let them fail.
Check your door sweeps. If you can slide a piece of paper under the door, a rat can slide its entire body. Literally. Install a new sweep. It’s ten bucks at the hardware store. Cheaper than a rat wedding in your attic.