Another way to prevent goats from climbing on car, or precluding them from any area, would be to install an invisible pet fence (http://www.invisiblefence.com/) around the car parking area as well as have each animal wear the companion shock collar.
I had to have the 1994 “Melissa Peterson guest host episode” after hearing her call the guys…I’m listing to Episode #9445 right now, it is great…20 years old and still holds up wonderfully!
Richard has a workable idea. In the Fall of 1956 I had a late lunch in high school with band rehearsal before lunch. I got tired of watching guys after the earlier lunches leaning against my beloved 1948 Chevy convertible in the parking lot. We had a spare 6 volt DC fence charger in the barn that I mounted in the trunk and connected to the battery via a wire with a toggle switch dropped through the drain hole in the bottom of the spare tire well. The high tension side of the charger was connected to the car’s body. I connected an insulated three foot ground cable with a 6" nail soldered to the end and placed the charger on a rubber mat in the trunk. When I got to school the next morning I surreptitiously dropped the ground wire through the drain hole and hammered the nail into the ground. Tossing the hammer in the trunk I’d turn on the toggle switch. From the time I turned it on to the time I left in the afternoon, every second that fencer would send a 30,000 volt pulse of electricity through the car. That day brought the first and best results, because it had showered a little and the parking lot was wet. The first buttock from first lunch that got within a quarter inch of my front fender contracted, extended and launched it’s owner into the car parked alongside. It was a beautiful thing to see. Soon there was a crowd assembled with the braver folks extending a finger to see if the car was truly electrified. The word spread and second lunch caught only one unsuspecting victim, but several finger shockers. By 9th period I was getting reports that my car was dangerous to which I replied, “Oh, did somebody get shocked? I really need to get the ignition checked!” Since we had band practice after school during football season I was alway late leaving the school and would wait until I could switch off the charger and pull up the grounding nail unobserved. The trick worked. I only had to turn the fencer on for a week. after that no one would get near the car. When asked how I was able to get in the car and not get shocked I would demonstrate (usually with the charger off) unlocking the door with the key held in my handkerchief, then opened the door the same way. With the door open Id take a running leap onto the seat, saying, “See, it’s easy, as long as you don’t touch both the car and the ground at the same time!” Only one other student, another farm boy, guessed my secret and he thought it to be so funny to swear secrecy. He heard the fencer clicking away in the trunk and knew the sound. So, unless he ratted me out, any of you folks who got your butt shocked when trying to lean against a 1948 Chevy Styleline convertible in the parking lot of the Lower Camden County Regional High School in Lindenwold, New Jersey during the fall of 1956 now know, “the rest of the story”. Photo courtesy Wikimedia Commons (unfortunately not mine).
My father did the same thing to keep a tenant’s dog from using his pickup truck as a fire hydrant. He used a log chain draped from the bed to the ground as his grounding mechanism. It only took once. I’m not sure the dog was ever the same.
I agree with Tom and Ray that putting 20000 volts on a modern car with multiple computers would not be wise. That said, most cars can build up a static charge anyway as seen when you get out of a car and get a shock - so it is possible that a fence charger might work. I notice that the Mythbusters always use rented cars for their experiments. Or you you get a few junkers and electrify them in the hopes that the goats would associate shocks from all cars. Or how about just build a climbing structure for them to climb on instead?
The BarMas invisible leash idea sounds best.