Forcing Flag To Be Unique In Drupal 7 In Drupal 7, using Flags (and possibly Rules or another contrib module) how can I force a flag to be unique for a specific content type.  I do not want to force users to manually 'unflag' content before 'flagging' a new node.  I would like reviously flagged nodes to be automatically unflagged once a new flag has been set.

The goal is to allow users to select a 'default node' by use of flags.  Only one default node should be allowed.

How can I force and automate flag uniqueness?
Drupal Rules has a Trim-A-Flag action that lets you set a 'queue' size, or a 'max' number of flags allowed.  If you set the queue to 1, you can force a flag to be unique, and have it automatically update when a new entity is flagged.

Screenshot below.