How do you keep a reining horse from anticipating the lead change?

A reining horse that anticipates the lead change — beginning the change before the rider asks, drifting toward the center of the pen in preparation, or breaking its circle shape as the pattern location for the change approaches — has mapped the pattern well enough to execute it on its own schedule, which is the opposite of the responsive, rider-directed performance that reining judges reward. The prevention and correction are the same: never change leads in the same place every time, and vary every element of the sequence that the horse has learned to use as a predictor. Sometimes continue the circle well past the point where the change normally happens without making the change. Sometimes transition to a trot or a collected lope rather than changing leads. Sometimes counter-canter for an additional circle before asking for the change. Sometimes change on the pattern location but occasionally skip it entirely and continue for another full circle first. The horse that cannot predict when the lead change will be asked learns to wait for the rider's specific cue rather than acting on location or speed as the trigger. Introducing the change from different locations in the arena — not just at the center of the pen during pattern work — further disrupts the horse's ability to anticipate based on arena position. Counter-cantering specifically is one of the most useful tools for a horse that anticipates changes, because it requires the horse to maintain the current lead through the location where it expects to change, directly contradicting the anticipated pattern. A horse confirmed in its ability to counter-canter willingly and for multiple circles has demonstrated the patience and responsiveness to the rider that prevents anticipation from developing in the first place, and maintaining counter-canter work throughout the horse's training career is one of the best preventive measures against anticipation returning.