I'm not recommending this, but you could get a fence charger from the farm supply store and hook it up to your car. But you would have to put it inside your car or the thieves will just disconnect it and then you can't get in either.
I strongly advise that you NOT electrify your car body. Here are a couple of reasons.
1. In many states this would by law considered a "MAN TRAP, and subject to criminal penalties.
2. Even in the absence of prohibitive law, if ANYONE, and innocent child "cutting through your yard, or even a thief attempting to break into the car, were to be hurt in reacting to a shock, or worse, killed as a result of the electrification, you would be exposed to tremendous civil liability.j3h.
Perhaps if you park upon a large steel plate or grating and attach one electrode of a high-voltage device to the grate and one to the car, a person standing on the metal in bare feet and touching the car might complete the circuit and feel a shock.
Another possibility that has been explored is to generate a huge static electric charge on the car, causing it to throw off scary-looking (and potentially dangerous) sparks as the static discharges to the air, ground, and nearby objects.
Rather than go through all of that, why not rent a garage to park inside and avoid the possibility of accidentally injuring someone?
Crystal