How to change default location for iTunes Library

You can set the folder location at Edit > Preferences > Advanced.

Note that changing the folder will affect future rips, but does not move any existing files. If you wish to relocate your library to the new location, you can use the Consolidate command.

Once you set the folder location to an external drive, never start iTunes without the external being turned on and accessible. Doing so will cause iTunes to revert back to the internal location.

I've recently moved my library to my TimeCapsule and plan to move it from there to my DROBO FS once it arrives. This behavior of reverting to the 'local' or internal location is an absolute pain. Has anyone found a way to force iTunes to maintain the persistence of the remote library path even when not connected or at least to automatically restore itself to the remote library path once reconnected? It is the 'preference' that has been set so one would think Apple would figure out a way to maintain this preference over time and disconnections.