How can I automatically mount an external HD connected via USB to Airport Time Capsule every time I connect to my LAN? I make Time Machine backups on an external 2TB HD connected via USB to my Airport Time Capsule.

PROBLEM

When I come back to home and I reconnect to my wi-fi LAN, Time Machine is not able to automatically reconnect to the backup volume (see image below).



QUESTION

Is there any solution to enable Time Machine to reconnect automatically to external backup volume when I come back to home? ATTENTION: I do not need a solution to auto-mount at login/reboot, but rather a solution to auto-mount when I reconnect to my LAN. Thanks.
Without writing you a full blown Mac App, the best I can recommend is the app MarcoPolo

As an addition/update to this, MarcoPolo is no longer maintained and the developer suggests using control plane if it is not working with your system.