In Chapter 5, Share and Network in Groups, do you remember when setting up groups that you were able to select how users were added to your group? You chose between open and request membership groups as ways for users to join your group.
Administrators and staff have an additional option for adding users to their group — controlled membership. This option gives you ultimate power over who belongs in your group. You can pick any user in the site and force him/her to be a member. There is also the added factor that once a user has been added, he/she cannot leave without you removing them.
You will notice this additional option pop up in your group settings:
Note that your group can be controlled as well as request. That ...