One observation, I think people in this post are looking at the term "Rim Protector" to mean players who will play great defense and prevent their man from penetrating to the rim. Its my understanding that when Ainge is refers to a "Rim Protector" he is talking about a big man who is capable or rotating away from his man in the paint and preventing easy high percentage baskets. I have noted in other posts that these are typically big men with at least average mobility and standing reaches over 9'2".
Examples in current NBA: D Howard, L Sanders, Asik, KG, Duncan
Examples in the past: Russell, Hakeem, Wilt, Mutombo, Shaq, Mourning, Ostertag, Smits