Farmers use something called Fresh Cab, rodent repellent. Can buy at Tractor Supply or other farm service store. I've been using it, so far so good.
Had a Suburban a while back that squirrels kept getting into the engine compartment and chewing wires. I mixed a spray bottle with 50% Hot Sauce, 50% water and a good squirt of dish-washing soap. Soap is sticky and stays on their feet, when they go to lick/clean it off they get the hot sauce. They don't come back. CAUTION - the solution is very caustic on exposed metal parts. Made everything look like it was corroded, but no squirrels!
