If you want to build an arena for the kids to ride broke horses in with the trainer, landscape timbers and non-electrified electric tape, makes a great fence. It's mostly a "visual" enclosure with a trained horse.... if you aren't turning them out in there, they aren't going to be testing the fence but it is sturdy enough that you could turn out for a while if needed.
My goal was an arena that I could safely ride in (I have kids, so the fence is about "you stay out of here" as well as telling my horse "you're stuck in here" if he should bolt) but be able if needed to strip the tack off my horse and leave him to go deal with a kiddo problem. I also wanted enough of a boundary that my kids could ride and I wasn't worried about the horse taking off with them and going for the road. Shop 3" x 3" x 8' Landscape Timber at Lowes.com
I used 2" tape and just screwed it directly into the wood since I won't be electrifying it. Gates I used treated 4x4x8 wood posts since I want them to be sturdy.
I wouldn't use it for breaking a foal though. I would put up a separate round pen of panels for that.