How do I learn to lope a correct circle in reining?

Learning to lope a correct circle begins with understanding what correct means: a genuinely round shape maintained consistently through all 360 degrees, a consistent loping rhythm that does not speed up or slow down without the rider's intent, appropriate bend through the horse's body that matches the arc of the circle, and the rider guiding rather than dragging the horse around the path. Most beginners discover that maintaining all of those qualities simultaneously requires more active guidance than they expected — the horse's natural tendency is to drift outward on one side, cut inward on another, speed up on the straight portions, and slow through the turns, and correcting those tendencies in real time is the skill the circle develops. The inside leg at the girth is the primary tool for preventing inward drift and maintaining forward energy; without it the horse falls inward and the circle tightens involuntarily. The outside rein prevents outward drift and maintains the shape of the arc; without it the horse bulges outward and the circle expands. The seat drives or softens pace. Begin the circle work at a slow, manageable lope where the corrections can be applied before the drift becomes significant, and focus on one quality at a time — shape first, then pace, then bend — rather than trying to perfect all three simultaneously. Use visual reference points on the fence or arena markers to guide the path of the circle rather than trying to feel roundness from the saddle alone, because a specific visual target gives the rider something concrete to ride toward at each point of the circle. The circle that looks and feels consistent from the outside develops from many repetitions of noticing deviations and correcting them before they become large.