My first thought is leveraging an electric fence like a trip line. The line has to be cut or tripped for something or someone to get in. I’d be very surprised if you can’t find a remote voltage monitor that can tell you real time if the fence lacked adequate charge. Heck, you could run a wire from the fence to an accessible location to manually check the wire with a fence tester and it its light goes red, you know the fence is down.