I have a barker.. he is highly reactive to other dogs. originally it was only larger dogs, but now it's just any other dog. We train in agility and I think the atmosphere of other reactive dogs has started to wear off on him.
Here are some of the things I do, cause the above stuff didn't work for me either:
1- we go to a weekly tiny dog class that is put on my trainer. While at these classes while others are working on puppy training, (I've been training with her for 2 years) I work on more advanced stuff and then reward calm and quiet. For me walking away from the issue DOES NOT HELP. So during this class we noticed that if Harley is taken away from me (the mothership, or in your case fathership
) he quiets down. By being with me he gets more tense and wants me to "protect him" he calms down and has learned that if he wants to stay with momma, he has to be calm and quiet, and episodes while in this class and he is taken away from me until he is quiet. This class allows him to build confidence with dogs his size who cannot hurt him if they are rough or loud.
2- If you know the dog he is barking at isn't going to eat him, do one of two things. While in a secured and fenced area, drop the leash. I can almost guarentee you he'll stop barking when he realizes you're not holding him and the other dog reacts calmly, he'll have an OMG WTH momment, and run behind you... if you're not in a secure area and you know the dog wont eat him, then stand there, do not move, or pull on the leash... let him bark (it may take 10 min the first time, so thank the other person for their patience) as soon as he stops say "thank-you" if he decides to turn towards you say "good" or click if you use a clicker. Give a treat if he comes all the way back to you (I'm assuming he'll be pulling on the leash to bark at the other dog). He will likely start barking again, just keep doing this. Eventually it will get worse, and then he'll realize that barking does NOTHING and he gets treats for calmly coming to you. Distinguish between "thank-you" meaning thanks for letting me know there is a dog, and "good" which means you stopped and stayed quiet so now you get a reward.
3- you mentioned you went to obedience classes and you had to stay far away. This is ok. A GOOD trainer will assure to accommodate and help you. I also attend agility classes weekly, and during this class the other 5 dogs stay in the ring, and I have to sit outside the fence. I started bringing a partner with me to help me reward quiet. We stay outside the ring unless it is our turn to work on equipment. I always pick him up to transport him from the quiet area to the actual ring. He usually growls in my arms. I've also started bringing a crate/xpen with me and play crate games while it's not our turn, today was his quietest day yet.
So one thing my coach told me is to pick one battle at a time, I allow him to squeal and growl thus far in my arms. So long as he isn't all and out barking I don't care. Once that improves then I'll attack growling, and squealling.
I'm sorry this is such a book, but it seems like you said traditional stuff isn't working. I am experiencing this right now. I've been doing the tiny dog classes for 4 weeks and I have seen a MEGA improvement. The fact that he is able to learn to socialize with these small dogs allows him to build confidence around other dogs too. (this class has an off lead portion to it where we let all the puppies play together).
Best of luck, if you need clarification don't hesitate to ask, you can pm me too. I have a huge weekly ritual I've been doing to try and work on this barking.