We fenced in our backyard with wood posts around the front/sides and T-posts in back (we want to move the fence back at some point) and ran a single electric wire around the bottom about 10" off the ground. When our mixed breed was let out there he figured out right way that the fence bites. After that, we were able to turn it off. When we put the chicken coop/pen back there, we put wire around the bottom of it because he has a high prey drive. He knows when it's on and when it's unplugged. Not sure if he can hear it or if he can smell it? It's odd though...if it's on, he gives it a wide berth, if we forget to plug it in, he digs around it.