Long story short I have a husband who hates my 3 indoor and 2 outdoor cats
as it is.  Constantly bitching about the cat litter, hair, clawing, etc.  Of
course his dog sleeps in our bed, with hair, dirt, etc, chews up things and
it's not a problem.....
Well we live in the country and he just bought a new blue truck, and my 2
stupid in/out cats INSIST on climbing on the hood and leaving slight
scratches and paw prints, but I can never catch them in the act.  Obviously
we don't have a garage so we can't lock the truck away from them.
What is a good repellant to use to keep them off his truck?  I've read about
this Scat Mat thing, but does it work?  What about the lemon-based repellant
sprays?  Would they work on a vehicle? I've even thought about getting a
motion detector.....I'm at my wits end.  If anyone has any tips, please let
me know.

(and please no comments about telling the husband to take his dog and truck
somewhere else.......I need the cat-hater's paycheck for at least a few more
years  :-)