My dog does not bark in all situations, but she does excessivly in the car and when around other dogs. I guess I should say that she used to. I tried alot of things, but what finally worked was a water-spray bottle. If just water does not do it, add a bit of vinegar to it- I had to because water alone did not faze her. The vinegar won't hurt a dog, but they don't like the taste, etc. This was something I read in a dog book that was highly recomended by our dog obedience trainer. If all else fails, give it a try!
Good luck, and let us know how it goes.