Help! how do I teach my horse to extend?

Q: “I’m having difficulty getting my horse to understand how to extend properly in any gait. Collection is easy enough but not extension. He does a decent walk and trot — his canter needs work but we’re only trying to do collection and extending in walk and trot at the moment. What happens now is when I ask for extended trot my horse runs — he puts his head up and panics a bit so then runs faster. He is getting fitter and stronger so I want to keep him going in the right direction but don’t really feel like he is getting the concept. When I do manage to stop him panicking I just get a normal working trot — there is nothing extra about it. I’m looking for ideas or exercises to do to improve it. I know some horses find it more difficult than others and think he is one of them. Any ideas welcomed!”
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