Thanks, Freckles, I think it sounds like a good suggestion.
Lately, to save hassle, the BO has put the horse in his stall out in the shed and left him there for me to halter up. It is easier to catch him, of course, but he gets VERY snippy and doesn't behave as well when I've got him in the crossties. I get the sense off him that he's...I dunno, offended. Or his feelings are injured. I don't know whether it's because he has to watch his paddock buddy getting to cruise around freely, or whether it's because he's missing out on the excitement of the chase.
I'm really tempted, if he's shut up next time I come to get him, to let him out so that we can play out our weird little ritual - because the end-result of that ritual is always that he consents to wear the halter (rather than being forced to wear the halter) and he behaves MUCH better if he thinks it's his choice.