Clowns and bubble coral

[Coralgurl]

My clowns are trying to get into my bubble coral. They are rubbing against it and looks like nipping a bit. If the hit one of its tentacles they go and rub against the sand or a rock. I don't have an anenome, tank is 6 months old. I know clowns don't need one, but should I get them one? I was thinking of a carpet anenome...thoughts?