This extension adds a custom data set to groups and adds a permission (CiviCRM Group Protect) to the CMS (At least it does for Drupal, not sure what it does for other CMS's).
The custom group adds a field for the Group: protected Yes or No. This settings can only be edited by users with the permission CiviCRM Group Protect. Only users with the permission CiviCRM Group Protect can add or remove contacts from a protected group.
The extension has been developed by CiviCooP, the development was funded by PUM Senior Experts. The extension has been tested on a sandbox and will be tested by the customer in the first quarter of 2016.