The new Ford automatic hubs also have a manual setting for locking, but I have never had to use it on my 2002 nor my 2008. I have also had the electronic shift-on-the-fly 4 wheel drive since 2002 and on my 2008 and it has never failed. The Ford 4 wheel drive system is one of the best ever made, IMHO.
2008 F-250 4X4 Lariat V-10
2002 Airstream Classic 30' w/SO #2074
2007 Kubota 900 RTV
1996 Ford Bronco
2007 Lincoln LT