On terms of service of some boards I browse says that all moderators and admins have the right for deleting or editing messages. And also they add that the terms of service may be changed on any time and the users must follow that text. You can also add that all the members are supposed to accept all the rules by becoming a member of the forum. I think if you write this rules then they must obey them because they accept these rules by becoming a member of that forum.
