I have to agree w/ Alex on most of this. There is a technology called Geoquip (although not inexpensive) that works well. It measures uncommon vibrations and cuts in the fence and hooks to your site alarm system.
You could also try a CCTV system that creates an alarm on motion (pixel change) and also hooks to the security system. This can create a false alarm nightmare if not set up correctly though. Hope this helps. Good luck.