In older releases, there was once an Advanced tab in the Remote Desktop Preferences Dialog (per this older tutorial: http://www.techotopia.com/index.php/..._Linux_Desktop), but now (12.04, perhaps recent releases too) it is renamed Desktop Sharing Preferences and only the basic settings remain.

Because I only intend to connect via SSH tunnel, I wish to deny all but localhost connections for security's sake. How do I access the Advanced settinsg? (Or at least, how do I set the deny localhost preference?)