Hi, Miriam
I made a rope halter (with advice from Danny Levin) and Freckles shakes his head a lot - even when I have no lead-rope on it. Until I figure out why, I don't want to use it much. Maybe a rope halter was used to gentle him?
I do know that a few weeks before I met Freckles, one of his half-brothers was killed in a "training accident." This particular colt was always "stand-offish" which he learned from his mother being over-protective (they had not bred her before and won't in future) and he spooked while being led between pastures. The lead rope wrapped around his front legs and tripped him. He broke his neck.
I think it's reasonable to assume Freckles knows about this, even though he was from the previous year's breeding, and was in a pasture away from the accident.
Whatever his reasons, Freckles seems less comfortable with a rope halter than with even his snaffle bridle. I have been taking him grazing in it hoping to create a lot of "positive association" and will have to wait and see on that.
He does know a version of the one-rein-stop, because at the walk I often ask (with seat and legs only) for smaller and smaller circles to a "bent" halt as a flexibility exercise. Most of our riding is still done at a walk as it's only been 2 months!
Other riders think I'm nuts when I refuse to "ask" for a canter, and only trot for a few meters at a time!