I have no idea if the following method has been tested or is effective but:
If attack is immanent drop down low enough to prevent the dog from grabbing your legs/crotch area and give the dog your offhand forearm. On impact shove your forearm as far back in the mouth as possible to open up the jaws while wrapping strong side forearm around the back of the dogs head and below the skull. Push and rotate out with weak forearm(in dogs mouth) and pull and rotate toward your chest with strong side arm. The idea is to strain/dislocate/break the neck so the dog either gives up or dies. Keep in mind you're doing this while the dog is thrashing on your arm trying to rip it off. A lot can go wrong, but if its all you got, give it everything you have.
Looks like I was late to the party. Jim in Idaho beat me to it.
Jim Corbett supposedly used a similar tactic to kill an attacking leapord. I still dont understand how he kept the cat in his face from disemboweling him with its hind legs.
