While Natalie does have a point, I’d argue that getting it in writing would be the politically sound approach.
You don’t want to have a trainer bringing in 30% of your revenue suddenly move across town and take all of their clients.
Usually non-competes will simply state that once a trainer or gym has terminated their agreement they will be unable to work within a 4-8-12+ mile radius of a club for 2 years. This prevents people from taking your customers.
now I understand. I think an attorney will be best to advise you here even though I am not sure whether there is an enforceable protection possible.
I know that Sue Hitzmann with MELT had this issue when she first shared some of her work with others which promptly was copied and used under other names. She eventually got it patent pending and trademarked.
I am not sure I understand your question: you train instructors in ‘your method’ but you do not want them to teach it? Why do you then train them in it?