Check out Fort Knox vs. the Barking Dog(from Benlog:
"The Barking Dog model is different. You still build fences. Maybe even a fancy lock. But more importantly, you get a well-trained dog, maybe even two or three for redundancy. And you assume that some of your fences will fail, because that’s what fences do when faced with smart intruders. When they do fail, and someone comes in, that’s where the barking dog comes in. Your defenses may fail, but your detectors will sound the alarm, allow you to respond and, hopefully, recover from the intrusion." (from: Fort Knox vs. the Barking Dog).