Expand the coverage of your electronic fence. Boundary Extension Kit gives you 500 feet of custom-engineered Ultra Wire, 50 boundary flags and 5 waterproof wire splices. This wire is specially engineered for electronic dog fences with electrical and mechanical properties optimized for your dog containment application. The wire is solid-core copper designed for optimum electrical impedance. It has an extra-thick jacket made of a specially formulated insulation material that is resistant to ultraviolet sunlight, moisture, ground rot, and corrosion. High tensile strength insulation greatly reduces the risk of wire breaks. Whether you have a genuine Humane Contain electronic dog fence or another brand, this is hands-down, the best dog containment fence wire you will find anywhere.