laughs . you can buy these from the local pet store.
Standard Radio Fence Works
The Transmitter plugs into a standard power outlet and emits a radio signal that travels along the boundary wire. You can adjust the signal to up to 15 feet from the wire. In most cases, a 1 metre signal field will be the best for optimal training. The lightweight receiver worn on your pet's collar picks up the radio signal and alerts him as he nears the boundary wire When your dog approaches the boundary, he hears a warning beep andif your dog does not return, he receives a static correction which is startling but not harmful.