Drive in the ground a copper ground rod and attach all three conductors of a 20 foot length of heavy duty extension cord to it. On the other end attach all three conductors to a insulated clamp. Clamp on to the electrified conductor of the fence and it will short out the circuit, making the fence safe for transit.
This would be the case only if you use the ground as the return path. But you don't have to do it this way; earth is not very conductive, especially in a hot, dry desert.
As a better example, drive two insulating sticks into the ground first. Then hang several rows of wires between them. Insert insulating spacers as required, so that sagging wires don't touch each other. Then apply three phases of 380V to wires 1, N, 2, N, 3, N counting from the bottom. Then continue upward in the same order if you have more wires. Any adjacent pair of wires will be under 220V. Any wires over N will be at 380V.
Such a fence is harder to short. First, it is isolated from the ground. If you walk up to it and touch any one wire nothing will happen to you. However if you start climbing and touch two wires... then you will get a shock of your life. Secondly, there are three independent coils of the transformer (three independent power sources) so if someone shorts wires 1 and N, the N and 2 are still deadly.
In any case, once the attacker starts shorting things the guard walks up to his Tac-50 and takes care of the invader. If there are two watch towers per mile the maximum distance the guard needs to shoot is 500 yards, which is very much doable against a man-sized target even with a common hunting rifle.