In the Dog Training posts there is a post about this - have a look.
We are trialing a hand held ultrasonic training device with one of our dogs that does this. She can be really scary if you don't know she will actually lick you to death.
Only started yesterday but so far appears to be having little effect. They say it may take a day or three for the dog to link barking with the ultrasonic buzz.
We found it on Ebay - it is called "The Cute Dog" ultrasonic training machine.
Border River Pet Resort