Damn, makes me glad I dont own a real car, though walking is only fun when its not raining...
Need a barking dog alarm system- it senses someone close to or touching the car (very sensitive to vibrations), and sets off the loud barking dog noise- and not the same set of barks each time otherwise the thief will realise its just a sound track, instead have random barks and growels from the same breed of dog, in short or long sections or 'tracks'.
My idea, but someone else can design and market it