I agree with whoever said to starry in small circles. Honestly, you could even start by walking next to your horse applying pressure with your fingers where your leg would fall on his side. Once he does that calmly, progress to a very small circle (only at a walk) where the lunge line is only as long as his body. Using the same cue of pointing where your leg would fall, lunge until he consistently walks around you (one foot planted) calmly. Slowly increase your circle at a walk. Take your time no matter what.
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