how do you respond to someone who doesnt respect what you are doing and slags you off in a practica he's running with your students
You could maintain your integrity and stay above it.
And if he comes up in a discussion, you could do your best to acknowledge him without trashing him or being dismissive. And, I think, you have to allow people to explore that path (by which I mean signing up with him) without judging them.
Maybe one day they will figure it out and come back to the fold.
Alex Krebs, Robert Hauk, Bill Alsup, Megan Pingree, all start off by telling people how many different ways there are to do AT, and even encourage people to take lessons from other instuctors.
This is all tough stuff to do (especially the "stay above it" part). But in the long run, I think it is the way to go.