How do I fix a mustang that has learned to pull back when tied?

A mustang that has learned to pull back when tied has typically had one or more experiences of being tied before it was genuinely ready to accept restraint — encountering the hard end of a rope attached to an immovable object while in a fearful state — and the pulling-back behavior that resulted was reinforced either by the halter or lead breaking and producing release, or by the horse discovering that sustained pulling eventually produced release through rope burn, equipment failure, or handler intervention. The first step in addressing established pull-back behavior is ensuring that the physical setup prevents self-reinforcement: a horse that can pull back hard enough to break equipment or pull free from a tie will continue doing so, and any correction program must use equipment — properly fitted rope halter, appropriate lead, secured tie point — that eliminates the possibility of breaking free through pulling. The correction approach most commonly recommended by experienced trainers uses a long rope threaded through a secure ring and held by the handler rather than tied solid, which allows the handler to release the rope completely the instant the horse steps forward rather than applying constant restraining tension that the horse fights against. This setup allows the horse to experience that stepping forward produces complete release — teaching it through its own choice of movement that forward movement is rewarded — rather than that sustained pulling eventually produces freedom. The process requires significant patience because pull-back behavior is often deeply established and has a long history of being reinforced before the correction program begins. Prevention is far more effective than correction: ensuring that a mustang's first tying experiences use breakaway setups or handler-held ropes rather than fixed ties, and that the horse has genuinely accepted light restraint before fixed tying is introduced, prevents the establishment of pull-back behavior rather than requiring its subsequent correction.