I see a lot of cowards here who would take up arms against a presumably unarmed perpetrator with the idea that it would be reasonable to do so. Personally I don't see it as 'what the law say', but more the fact that the punishment nowhere near fits the crime. Yes, I understand the safety issue...but if you're leaving vehicles outside and have no fence, motion detectors, or proximity alarms (on the vehicles) you are leaving the door open, so to speak. It's also highly likely that 99% of you goofballs who suggest wiring the wheels hot, swinging a solid object, or racking a shotgun would actually do anything if it came right down to someone coming into the yard. It seems unreasonable to me to suggest such things when you wouldn't carry them out yourselves. The internet if full of cheap talkers and people who find it extremely simple to type out their carnal fantasies. Quit feeding each others' desires and come up with some intelligent ideas.
This being said, a simple case of good old fashioned surveillance or deterrance is a more feasible option and legal on your own property. Finding an angle to set up motion detector 'game cameras' is an excellent choice if one doesn't make a production out of the installation or places it/them in inconspicuous locations. Hell, even a video camera set on time lapse and placed in a window would probably do the trick. Personally I have used my cameras on our apt building to aid local LEOs and even the landlords to get folks evicted and guests criminally trespassed from the property. Motion detector cameras with IR illuminators make it easy to see someone dicking around in the shadows and the fact that they're wireless makes it easy to place them. They record on a second PC dedicated for that purpose. When someone walks by, a timer turns on the camera as long as there is movement and records for 4 minutes after the last registered move. Cost me a total of $300 for the cameras, which I guarantee is a lot cheaper than bailing out of jail for assault with a deadly weapon...not to mention the lawsuit that would follow. Besides, it's a new toy to play with and is totally cool.
I wish you luck in catching your bad guy. Just do something smart, would ya?