I have a 7 year old male cat that loves laying on the hood and roof of my truck. I've smacked him off a few times (not hard enough to break anything or scratch my hood!) but he doesn't get the point. I love the kitty, but what'll I do about this? I've heard of these ultra-sonic motion-activated whistles that cover a 20' radius that I could bolt un in the car-port above the truck. I've also heard of some kind of gel that you put down wherever you want to keep the cats out of. What's the best solution? THANKS!