Hi,
I had a similar problem with car damage. So I bought cctv camera. But that did not help cause I could not catch the guys.
Then I came across these guys at smsVideoGuard.com They started watching my cctv camera and guess what, I caught them in the act. I would really recommend them and they are very affordable. A dollar a day for the security guard to watch your cctv camera. They don't record anything but just act when there is an incident, like a real guard.
I hope it helps you, it helped me :)
Cheers