The best thing that somebody can do is copy exactly what you're doing.
Whether it is your business model, a product you offer, your training programming, or content - let them copy and let them use everything.
One thing that someone who copies you will never have is the seed that brought forth all of those ideas. While they're picking up the fruit that your tree drops on the ground, your laying your roots deeper and solidifying find your position.
The copycat will never innovate; all they will do is copy in order to make short-term gains. They had more than enough opportunity to collaborate with you to create something unique (and better) than what already existed but they passed it up to selfishly pursue a small piece of the pie.
What they fail to realize is that the more they copy you, the further you become ingrained into their actions and their thoughts. While they are sitting there watching every move you make trying to duplicate, time is slipping through their hands as you are slipping further ahead
If you are afraid of losing to a copycat, you may just be a One-Trick Pony that needs to add more depth to what you're doing so it is easy to tell the difference between the knock-off and the real thing.