Providing security for a sensitive item is implemented using geo-fencing. A geo-fence may be established as a dynamic virtual perimeter defining the maximum allowable distance between a sensitive item for which security is provided, and a security providing entity. The sensitive item has a first trackable device associated with it and the security providing entity has a second trackable device associated with it. The first trackable device and the second trackable device are paired to each other and tracked. The dynamic virtual perimeter may encompass and move with the moving location of one of the trackable devices. A notification is provided when the first trackable device or the second trackable device is out of the virtual dynamic perimeter. The sensitive item may be a bank cash cassette and the security providing entity may be a person responsible for the bank cash cassette.