Why do you have the rope tied around the neck and then run through the halter ring as opposed to a normal lead line which is snapped into the halter, or a ropeleadline that is tied into a rope halter? Your method is intrigueing.
just today I was visiting a friend who;s horse was tied and eating from a hay net, and was standing about 4 feet behind him looking for hip irregularities (lameness inquiry) when he suddenly , without any obvious stimula, started to pull backward in a panic, nearly sitting on his butt. Naturally, I was backing away from him so fast it was amazing! The owner could not get in fast enough to pull the slip knot, but she was finally able to get his mind out of the panic with "whoa, whoa" and such. I had never seen a hrose pull so suddenly and so violently. She said she just deals with it by being nearby to undo the knot. H m m m. . . That sounds a bit odd. but I did not say anything.