This reminds me of a training episode I watched on tv last night.
I won't say who it was....to keep it neutral.
I have used a method like this and it does work.
Anyway.....this "person" said to work with your horse on the ground before you ever get in the saddle. They said to train your horse to do bends. Pull back gently on the rein/lead rope asking your horse to bend his head to that side. Bend the horse's head around constantly to the left and to the right from the ground. Bends that resulted with the horses nose touching the stirrup. The horses poll must stay lower than their withers. That a horse raising its head has more control. Keep them bent for a few minutes and once a horse started to give a little slack in the lead rope/rein then immediately let go and praise them then bend them again and wait for the slack until the horse was supple and easy to bend.
If the horse moves away or in circles...follow them for however long it takes.
This is for training in the saddle. While in the saddle do the same bends. Pulling gently back on the left rein asking the horse to bend down and touch its nose to your boot or stirrup and vice versa. Doing this several times and waiting for the horse to give some slack in the rein. Eventually you want it to be a fluid easy movement where the horse does it at the slightest pressure from you.
This is effective in learning one rein stops and corrections. If your horse tries to run away while you are in the saddle or tries to rear or buck you can immediately execute a bend/one rein stop and this throws the horse off balance, causing them to move their rear end/crossing the hind legs and stopping the offending action.
Usually people pull back on the reins and push their feet forward and nothing happens or it takes awhile. Once a horse gets their head up your playing tug of war with a 1,000lbs or more. This also results in the horse getting hard in the mouth and ignoring rein commands when they try to take the lead or bolt or when they spook.
But you must execute the one rein command as soon as they start the offending action or it may be too late to do anything or can result in the horse being thrown farther off balance then what is needed.
It's a lot like nuts and bolts - if the rider's nuts, the horse bolts! ~Nicholas Evans