A power fence is a psychological barrier that keeps farm animals in and wild animals and vermin out - even over long distances.
A pulsed electric current is sent along the fence wire, about one pulse per second, from an energizer which is earthed (grounded). When the animal touches the fence it completes the circuit between the fence and the ground and receives a short, sharp but safe shock. The shock is sufficiently memorable that the animal never forgets. If the ground is very dry, the fence may require an earth return wire.
A power fence is a psychological barrier so doesn't need great physical strength. However, it must be well designed and constructed to absorb some pressure from animals, snow and wind. The energizer must have enough power for the length of fence and for the animals being controlled.
It is important to understand how resistance of different wires and the number of wires can affect the performance of your electric fence. Resistance (ohms) measures a wires' ability to conduct electricity (current). The lower the Ohms, the more current it will conduct. It has the same effect as the friction of a water pipe has on water flow. Voltage in electricity is like pressure in water. Electric current (amps) is like water volume or flow.