[Houman21]

That video cracked me up.

I think you should let 1000 mice loose in the parking garage and the cats will be occupied
and not have time to sleep on the hood.

Or....

Stop driving the car so it's cold and they won't want to sleep on the hood.

I kid

I have two cats so they don't bug me as pets but the last place I lived at, the neighborhood cats would pee all over the front door and on my wheels - so I feel your pain. Mothballs and all of the remedies never worked for me.

I ended up sticking an old sony dv camera (the ones with night vision) in my car so I could see what was happening overnight. A friend then built a shield that he attached to an Arduino that would emit a high pitch ultrasonic sound that would irritate the cat.

While cool in theory, it kind of worked, but it drove my neighbors dogs ape shit as a side effect so it wasn't a great solution. I ended up moving (not because of the cats) so we never played with the Arduino solution further and he ended up using it for something else.

One thing that would be beneficial is seeing exactly what the cats are doing, once you know that - you could start planning a decent solution. We toyed with using the arduino to trigger predatory sound efx (dog growls and such) through a speaker but never built it.

OP it sucks you've got to deal with this and it's going to be a tough problem to solve, even if you went the inhumane route and tried to 'end' the cats, another would just take its place.

Good Luck Man