if it's a good halter (with a safety that will break when a force greater then what it's designed for is applied to it) he has no problem and is doing the only sane thing he can. if he has to run after his horse time after time the horse will soon figure out it's faster then him.
a good halter, constructed properly, can't hang a horse, if it's applied properly as well.
and another thing: the best way to make enemies is by telling people what to do in an inpersonal, off the big ivory tower, kind of way. leaving documentation would qualify as that. why don't you talk t him, ask him why he leaves the halter on and then you can say you saw horses get strangled. inform him of the fact that there are safety halters, but don't tell people what they can or can't do, they'll just get ticked off. and then it wouldn't be equine safety, it would be a human safety issue.
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