You can do the trick by putting the wire inside the hose or by using an armored cable. This would prevent unnecessary things that might happen. You can also use a circuit breaker for safer electrical system.

I think it is better to use armored cables and waterproof switches for electrical system rather than putting it on the fences. You can check some certified electricians in your local area to ask advice. They can give you more reliable information with regards to electrical system in your house.