Old fashion spring trap. Micky can be greedy so I've had good luck with wedging a piece of paper or cardboard where the bait goes - and smearing the peanut butter on the paper. Never have had the bait stolen since.
Last spring I heard what sounded like a couple of mice wrestling somewhere in the belly pan of the GT. My wife and I tried to pinpoint the noise and could only narrow it down to somewhere in the center pan by the gas tank. Whatever it was I figured they were in there chewing on the wire harnesses and fuel lines so I quickly pulled the center cover and didn't find a thing - no damage either. I went for a "brisk" drive with the cover off to scare them out. Not sure if that did it but I set some traps by each wheel using peanut butter and caught one that night. I keep a trap by each wheel now and catch one every month or so. Not sure on the cost of a wire harness, but my guess is about 500x the cost of the traps.