A dick in the ass every now and then doesn't hurt.

This couple fucks their asses every now and then, but it's very rare that they do, because she doesn't like it and he doesn't like it either, because he can never put his whole dick in it and fuck it deep. But to train the ass thinking about a future, they play a little. He puts his dick in her ass and she complains but holds on, he moves a little, he takes his dick out of the ass that is open, and they keep trying, until one day he can put his dick all the way in.