Methods, systems, and apparatus for defining, generating, utilizing, and/or detecting a geo-fence are described. A definition of a geo-fence is obtained, the geo-fence being defined based on a first geo-fence criterion of a plurality of geo-fence criteria. A trigger is obtained, the trigger generated in response to a change in the geo-fence criterion. One or more boundaries of the geo-fence based on the changed first geo-fence criteria are redefined in response to obtaining the trigger.