you need to have a visual barrier.... horses often get caught in wire fences because they don't respect or see them... maybe just put boards on the top rail? If not I would suggest electric. Make sure the fence is NOT stretchy or bendable, they will figure this out and rub on it or squeeze through it, which will cause it to stretch more. In my opinion wood is probably the best fence (but I know too expensive), but only if installed properly and with lots of rails, not just three. Wire works, but I've seen so many horrible injuries, that to me it's not worth it. My mare coliced and panicked and went through a wire fence... she cut her back tendon in two. I've seen completely skinned hind legs due to wire... A panicked horse WILL go through whatever you put up.... sometimes it's better if it has some "give" in the fence for these situations. I wish you luck, and i'm sure that there is no such thing as a perfect fence, everything has a drawback. I think just wire would be bad, if you absolutely must use it at least reinforce with rails or electricity.