Yeah, I think I may do that. I didn't use a signed letter, but I did that with Dr. T regarding ex-MC. I guess it hadn't occurred to me that if I had terminated with a therapist, they wouldn't still have communication rights. But months after termination, I emailed ex-MC something, and he BCCed Dr. T in his reply. I only found this out when I said something about ex-MC getting back to me, and Dr. T saying, "Yeah, I saw." I immediately revoked the rights (and he showed me the updated letter with them revoked).

Is there a particular form the signed letter needs to take? Like legal phrasing I need to use?