The Art of Taming and Training Wild Horses
The Art of Taming and Training Wild Horses – How to Lead a Colt by the Side of a Broken Horse.
If you should want to lead your colt by the side of another horse, as is often the case, I would advise you to take your horse into the stable, attach a second strap to the colt’s halter, and lead your horse up alongside him.
Then get on the broken horse and take one strap around his breast, under his martingale, (if he has any on,) holding it in your left hand.
This will prevent the colt from getting back too far; besides, you will have more power to hold him, with the strap pulling against the horse’s breast.