So far as I know, the BLM does not have any regulations about not having arches over the gate. I don't see any reason why they would not be okay. I don't consider them any more dangerous than any other type of fencing. A horse could injure themselves in a padded rubber room. LOL. Even for a BLM, unless they lead, they best way is just to back up the trailer to the gate of the roundpen and let them run out into the pen. At that point, the arch would be too close to the trailer for the horse to hit and when you take him back out of the pen, he should lead quietly or be trained enough to be ridden. Plus, I think you have to have the arch thing for the gate to keep the other panels standing when you open the gate. If it wasn't there, the other panels could move or fall over when you opened the gate. Hope I helped. Are you getting a Mustang? If so, I totally want pix.