My thought was something like a dog with a rescue organization, if you could arrange to take it home on trial for a few days and return it if it doesn't work out. Some dogs are fine with chickens almost without training (either someone trained them in the past, or they just aren't interested in...
Some labs are fine with chickens and pet rabbits, and staying home rather than roaming the country. I would say the problem was with your neighbors and their lack of dog training (and maybe lack of fences), rather than the breed of the dog.
But that is a good reminder that any breed can be a...
Of course the dog needs to not hurt the chickens, but it may not even need to try to guard them. Just trying to "play" with the fox might be enough to make the fox go away!
Maybe look at what adult dogs are already available in your area, no matter what breed, and try one or another of them...