If putting a proper security camera at the driveway is not possible how about a game camera. They take a picture when a built in motion sensor detects something moving. They are completely self contained. Hunters use them to keep an eye on the game animals when they aren't on the property. You will want one with an IR flash and some have movie capability if you desire that. They will run a around $100 US on up. I think between the baby monitors and a game camera for evidence of wrong doing you could make a case pretty easily if someone were to try something again.
Apparently, you just aren't professional enough to drive on three wheels: (Skip to 0:17)