Get a Victor rat trap. Bait it with peanut butter. Attach a chain to it and nail or bolt the chain to something big.
Where I used to work in Seattle the traps kept disappearing until we chained them to racking or the leg of my desk
They were using my bottom drawers for a bathroom. They quit after the trap caught three of them. Big as cats.
I have a Jack Russel at home... No rats there.