Maybe re-connect the on-board alarm with a hidden switch you can use to switch it off when you are driving.
The problem with trying to resolve this type of incident through confrontation or the police is the worry about retaliation. I had an incident at my home about 2 years ago. I was outside my house with my dog late one night but was in a shaded part of my side yard. I heard a comotion down the street and saw three kids coming towards my home obviously drunk or drugged. One was particularly vocal and as he got to my driveway he pulled out a knife and slashed the garbage bags at the end of my driveway. A real mess. I was mad as hell and ran down the driveway to confront them along with my dog. Yeah, I realise it was stupid but it was a reaction to the situation. When I told them I had seen them slash my garbage they got all defensive and tried to deny it. One even tried to put the garbage back into the split bags. They said the didn't want any trouble (I think they were so surprised at being caught and the dog probably helped) so I decide to back off and let them go.
I got the dog inside and then followed them in my wife's Camry making sure they didn't see me. Eventually they went into a house a few blocks away. Next day I went around to the house after work. Dad answered the door and I asked if his son was home. 'Knife Slasher' himself appears, dad goes back into kitchen but within hearing range. Kid's eyes are as big as saucers. I remained calm and said we had met the night before. He told me he hadn't been out. I asked if he had a brother that looked like him and he said yes. I said well maybe it was your brother, but either way I didn't appreciate my property being vandalized and related the incident. I told him we had had a number of problems on my street over the last few months and my neighbour had taken to keeping a video camera handy. Last night when he heard all the noise coming down the street he used it to film what had happened. I told the kid to tell his brother that if we had any more trouble from him or his friends whatsoever, that tape was going to the police along with this address. Of course I was totally bluffing about the video camera and film, but I never had any trouble after that.
