First of all your material is protected through the copyright, but in order to collect any damages the copyright needs to be registered, so do that first. You should have a good argument because you have invoices they paid for training in the material so if they copy it fairly closely you could collect damages. A trademark isn't going to give you much protection on the material, trademarks are really only good for your brand and your logo, if part of your material is the brand then trademark it.

There are two other paths you can look at also. First ask the client about it, see if they are willing to partner in some way; for instance you could license your copyrighted material to them for use with their own clients. Second think about using a Creative Commons licence on the material that allows them to use it but drives their clients back to you; take a look at how Strategyzer has done this with the Business Model Generation Canvas.

I am an attorney: nothing in this post should be considered legal advice. I am an experienced intellectual property attorney and a registered patent attorney.

You have a few options:

1) You could try to register a trademark for the name of your program, if you just want to make sure that competitors use a different name.

2) You could try to patent the method of your coaching program.

3) You could register the copyrights on all your coaching materials so they can't make direct copies of them.

4) You could include nondisclosure/noncompetition language in your coaching program contract so you can sue any clients who re-use your coaching program materials for their own benefit.

I have worked with therapists and life coaches on similar matters and would be glad to discuss it with you on a call.