How an Electric Fence Works
All electric fences have two parts, an active part and an inactive part. The active part consists of the positive terminal on the electric fence charger, the insulated electric fence wire connecting the electric fence charger's positive terminal to the conductor (polyrope, polytape, etc.), and the actively charged electric fence conductor that runs along the fence. The inactive or "neutral" part consists of the negative terminal on the electric fence charger and all the conductors connected to it. In the traditional setup using a ground rod, these are a wire connecting the negative terminal to a ground rod, the ground rod itself, and moisture in the soil running from the ground rod over to the fence.
The target animal gets a shock when it unsuspectingly provides a bridge between these two systems. That is, when it touches the active wire a charge passes from the active wire through the animal's body, through its feet, and out its feet into the water in the ground (dry soil cannot carry a charge but water can). Using this water, the charge travels over to the ground rod, up the ground rod, along the ground rod wire, and over to the negative terminal on the charger, thereby completing the circuit.
But suppose there is no or extremely little water in the ground, as often happens in parched regions. Then the animal will not get a shock, because there is nothing to carry the charge from its feet over to the ground rod. The same thing happens in deeply frozen ground, because ice in contrast to liquid water cannot carry a charge.
In both these cases, something must be done to remedy the situation or the electric fencing won't work. One's first impulse is to get a more powerful charger or perhaps increase the number of ground rods. However, these are not ideal remedies. They may improve matters, but they don't get to the heart of the trouble. The best answer, and the only one if the trouble is really bad, is to replace the absent or frozen soil moisture with something else.
Suppose, for example, that you string another conductor on the electric fencing that is 6 inches to a foot away from some charged conductor. This conductor, however, is not charged, because it is not connected to the charger's positive terminal. Instead it is connected to the charger's negative terminal, and things are arranged so that it does not touch any active conductor. Then, when the animal comes along and touches the active and inactive wires at the same time it gets a shock—with the charge passing from the active wire through the animal to the negative wire and over to the charger's negative terminal, thereby completing the circuit.