I am back to the university that I got my PhD, as an assistant professor now. My mentor is now the department head (but not when I was a PhD student). Given that we are working on similar subjects, I will always send all of my work that relevant to him and will have him as a co-author. Even if the work could be done without him, he is still experienced and may have useful comments. I am afraid this would be considered as not independent, and affecting my tenure applications. What could be the evidence to show I am independent?
My field is health-related, so that usually there are collaboration works.