I prefer a good electric fence with actual wire and not the poly stuff. Poly has fine wire in it that just doesn't carry the voltage, rots in the sun and breaks when blowing in the wind. If you make the fence hot (many don't) and keep it hot through proper maintenance your horse will not get out.
Safe isn't really a word when it comes to horses. They are the most self destructive critters I know and will find a way to hurt themselves on every fencing material known to man. I've even seen two horses cut up by electric tape by somehow getting it wrapped around their leg instead of breaking it.