This thick wall 500-foot under-ground cable is insulated wire or underground cable. It's a product that is used often when building electric hi-tensile fence systems. Powerflex Fence recommends include using the cable for your connections and your grounding system. It works well under gateways. It can and should be used for your lead out wires and jumpers.

Insulated wire, also called underground cable is generally class III coated wire inside insulated sleeves or jackets. They are very tough and come in both single wall and double wall configurations. 

UV-Stabilized MDPE Class 3 0.99" Soft Wire