I didn't mean it to sound that either of you were being cruel, I was just stating the fact that SOME stallion owners tend to do this and it is not a good form of management.
Is this guy just standing there quietly with an erection, or does he call out and act obnoxious on top of that??
If they just stand there quietly I tend to do nothing, but if you are at a horse show the best remedy is working them. Exercise will generally make them retract, although I have known stallions that will continue around the arena at a canter and still have the erection. Those are usually young stallions though, and is not normally the way it is. I even know of a TB stallion that went around being schooled over fences with an erection......but that made him FINALLY suck it back up. How annoying would THAT be?? LOL!!!
If he is being loud and obnoxious smack him with a whip or the end of the lead in the chest and yell 'quit it' or ' no talking'. Keep doing that until he is quiet and then leave him be. He should soon get the idea. You may have to just truck him to a few places to be handled/worked around other horses to learn that he is not there to breed and is there to work so he gets the idea. It may be tough and take a while though as this guy is older. Sorry, I wish I could be of more help.