May be time to try something like the SportDog bark collar. I have one of these for my Lab. Uses elec. stimulation rather than sound, and has three types of correction, depending on what is needed for your dog.
My lab will usually only bark once before the collar kicks in- it has a mode that sets itself to the intensity of your dog's bark, and will respond if the dog barks at that level again. There are also user-determined settings, and a progressive mode that gets stronger with each successive bark.
My dog will bark at a lot of things while outside in her kennel- deer, rabbits, birds, you name it. With her collar on, usually one bark is all you are going to hear from her. In the house, no collar- I want her to bark if someone is at the door, or whatever.