Nothing is ever guaranteed 100%.

If you're in the US, read up on HIPAA so you know what's a violation and what's not.
https://www.hhs.gov/sites/default/fi...tal-health.pdf

Find a therapist you trust.
Ask how they ensure confidentiality.
Figure out what you're OK with. Are you OK with consulting about you? Do you not want someone who's under supervision so they don't have to talk about their cases?

I mean, that's like asking how to ensure that doctors, nurses, dentist, etc. are going to respect your privacy. Most just do because that's drilled into their head in school and work and that's part of the job.

And what protections are you looking for? That seems a weird word choice. Do you mean recourse? http://www.apa.org/helpcenter/confidentiality.aspx