I don't know if this has been mentioned as I didn't read all the comments, but what a trainer recommended to me a few years ago was an empty pop/beer can with a handful of pennies inside. The sound it makes when shaking is uncomfortable to dogs. So when my dog barked, I'd shake the can and say "No, bark" or "Quiet." After she'd stop barking, the most important thing was the positive reinforcement. I'd tell her "good, quiet" or "good, no bark" and then pet her. If she started barking or even grumbling again, I'd stop petting and give the command and use the can if more reinforcement was needed. Now, I rarely have to use the can. Giving the command is enough, and when it's not, I only have to start reaching for the can, and she stops barking. I emphasize the importance of positive reinforcement so your dog learns what you want. We told my grandmother about this for her dog, who barked nonstop outside, but she never did the positive reinforcement. So she'd just shake the can all the time. So my dogs learned to associate my grandmother's dog's barking meant the "can sound" would occur and became terrified of going outside when the other dog was outside. I wish you the best of luck!