why aren't 'know networks' gps-geofenced on smartphones? You have GPS, if your previous 'known network' (say, home) was in location X, it should not automatically connect (or even try to connect) to it at X + 20 miles. This way you should be able to keep your phone from connecting automatically to (or even looking for) a network that shouldn't be there in that location in the first place, and if you always tether to…
For that to work the networks themselves would have to securely distribute a list of locations, or it would have to be configurable on the devices. Many business and educational networks (like eduroam) span multiple locations. Even my "home" network is available multiple places (home, cottage, boat...). Smartphones mostly use wireless networks and cell towers to determine their approximate location, which can be easi…
If the user does not want to incur the GPS battery impact triangulating with cell towers already should give you enough location information not to look for your home network at work, or the network you saw in Spain last month when you are in the Netherlands.
And finally obviously everything can be spoofed, however I don't think it's reason enough not to have a minimal set of protections: the user can decide how much battery to dedicate to the task (i.e. no checking, cell tower checking, gps checking in increasing order of impact)