I've used concrete reinforcement mesh panels for garden fencing, but for the reasons Margo said, I wouldn't use it for horse fencing (of course, for the garden I WANT the non-galvanized, pre-rusted stuff, and I REALLY would not use that anywhere the horses would make contact)
Going just a bit off topic...
Back when we were amongst "The Young and the Horseless," Keith and I put up a garden fence using a 50 foot roll of reinforcement mesh. This stuff wants to retain the curve of the roll, so we rolled it out onto the lawn to flatten it out. In a memorable brain fart, we rolled it out curl side up instead of down. Realizing our mistake, Keith reached for a brick to weigh it down, but let go of the roll (I was holding the end.
As soon as he let go, the entire rolling came springing back toward me. Now, a savvy do-it-yourselfer would have jumped out of the way, but no -- I just held out my hands to stop it, not realizing the strength in that roll of wire. My hands did not stop it, and it hit me full force in the face. Luckily, I only got a nasty gash on my nose, but it was quite a shock, and even more so to Keith, who thought I was seriously hurt.
Ah, well, lesson learned!