Which livestock are most difficult to fence in?

Without a doubt, goats and pigs love to escape. Cattle, although large, can be safely kept behind a single hot wire.

Are metal or wooden gates best?

Metal gates are much lighter than wooden gates and don't warp as much. But wooden gates look better. It's a matter of choice.

How much power does an electric fence use?

Very little. It depends on the length of wire but it will only cost you cents per day.

Do I need yards?

If you have cattle then you need yards. Not everyday but if you need to handle a scared animal it's much safer, for you and the animal, if it can be confined.