rodent proofing a garage

Thanks guys, the ideas give me some ideas until the weather warms up enough to go outside. I tried Fresh Cab (rodent repellant) and checked a couple weeks ago and found one mouse turd (only one) in the trunk. We have 2 cats outside, but the one is a male and got in the garage this summer and sprayed something and the garage still reeks of cat pee. Maybe I shouldn't chase the snakes out when they get in, but I don't know if garter snakes eat mice.