It might benefit both of you if you work on this with another horse, who will do changes routinely, until it is second nature for you while at the same time have the pro work with your horse. Every horse will do it naturally – the hard part is getting them to do things when you ask. One of the hardest things for me to get right, is knowing where my horse’s feet are when I want to ask for a change. Do you work on this on a straight line or a curve? Maybe having someone in the ring holler “now” when his feet are in the correct place will help you feel when he is properly prepared for a change will help?
One of mine will only do lead changes nicely for serpentines or figure 8s, and refuses (adamantly) to pick up his left lead when working on the rail. No apparent reason, and he is naturally left handed (hoofed?) and prefers to take his left lead when loose. My conclusion is that I am throwing him off balance in some way, making everything more difficult than it needs to be.
It is possible that your horse gets “wild” (your word) for some similar reason.
It is never the horse's fault