In addition to the Hitch lock (see Hitch Lock gellery) I've added cable locks to both tires.
The cable lock goes through the tire and around the axle.
The cable going around the axle.
Since I use a DeWalt drill to raise and lower the tongue jack I've removed the tongue jack handle and replaced it with a 1/2 inch socket. Of course if a thief had a 1/2 drive he/she could raise the tongue.
Raising or lowing the tongue is a litte more difficult if the socket in not in place which I do during prolong storage.