There is someone at the end of my street with two dogs that they keep outside all day, and those dogs are barking all the time. I can't hear it from my place, but I would be furious if I lived next door. I don't know how the next-door neighbors cope.

I have seen machines advertised for this problem. They emit some high-frequency sound that is annoying to the dog, but which humans can't hear. I think the idea would be to turn it on when they are barking, and off when they are not, so that they associate barking with hearing the unpleasant noise. I haven't used one of these but I would look into it further if there was a dog barking near me all the time.