I don’t think anything is entirely horse/idiot-proof, but I would definitely be nervous about the low stall fronts. My current horse is an escape artist and a very good fence jumper and he would have a go at those.
I once left him tied in an 10x10 outdoor wooden yard with a hay net as I was going to ride another horse in the area that was about 30 yards away - completely visible from where he was. The yard was at least 4’ high with 4 solid rails, with 1’ drop on the arena side (it was built on a slight slope). As soon as I rode off on the other horse he jumped out and joined us :eek: - somehow snapping the twine he was tied too.
I’m about to get some big outdoor sand yards built at home (yay!) and they will be 5’ railings with a hot tape extension on top - total height at least 6’.