Depending on what you want to do.
Revenge:
Get doe piss or fox piss from a hunting store and pin it through their car window.
Get glazing compound from hardware store and flick it on their windshield. It looks like bird shit so when they use their wipers they'll haze the shit out of their windshield with tiny scratches.
On hot days bologna on their paint will peel it right off.
Surveillance:
Get a motion sensitive light and an old iPod. Load cloud cam on the iPod and point it towards your car. You can monitor and tape the results on your computer.
If all else fails, bear traps have never let me down.
