You know what i would do in your situation. sit there one day, watch the little crow barstewards clean one of their cars for 7 hours straight, full cut polish and wax... then wait for the right time, about 10 mins after he's completed it, taken several photos, told his mates to come over and take a look, then take a large watery @*!# on the top and bonnet. then just walk away like yo, you shouldnt have parked it there in the first place.
It stopped me parking under a certain tree lol, it might stop them infesting in your place!