I think a sub such as Rodney would need to understand that his top is not only not going to take any shit from him, but nor from anyone else either, and that he remains constant in this fact before Rodney can feel comfortable enough to give himself over completely to this man's protection and love.

Oh truer words were never spoken. This is why I love Xanthe's John so much! He's very consistent and worlds more patient with Rodney than in canon. Rodney won't give himself over to anyone that can't handle his shit and I think Rodney wants to be controlled in that way, so he CAN give of himself and know that he won't be "given up on". I also agree re the pain thing. John's commitment is 100% and he will expect no less from Rodney. He needs it to know they can have the relationship he can see being. Rodney doesn't quite see that full potential yet, but John does.