So I have sensors around my house pretty much tell me if unwanted persons come into my yards. However I would like to find a way to protect the fence without spending a huge amount of money, I would like to have some kinda trigger device that birds, cats wont set off the fence is wood so attaching a sensor to it wont help so looking for inexpensive ideas to detect the fence area without getting a million false alarms. Due to the nature of my yard sensors they wont pick up cats or dogs just people. But Getting a fence protected brings up the question how, and how to do it reasonable. I can build anything I prefer that it possible. Thought of trip lines but then they would need to be set all along the fence and have a trigger setup not easily done. Ideas again please keep in mind not looking for microwave, shock sensors or fiber optics all would be way way out of range.