The GeoFencing feature that is currently supported by the arduplane code is now being tested in the arducopter code. So you dont have to worry about your arducopter flying away. The Geofencing feature will essentially return your Arducopter back if you fly outside of the fence radius.
Please note this has not been extensively tested just yet, so use it with caution. More info here
Please note this has not been extensively tested just yet, so use it with caution. More info here