Your neighbors don't seem to want to train their dog, so it looks like YOU'RE going to have to.
I suggest using an air-horn.
Cabela's -- Eco-Blast Sport Air Horn
Choose a command to shout when you want the neighbor's dog to shut up (QUIET, STFU, HILLARY, etc). When the dog barks, shout at him. If he continues, shout again, and give him a blast of the horn.
If this irritates your neighbors, GOOD. You may have to explain to them that they have had way more than enough time to train him by now (air-horn training takes five minutes) THEIR way, so since you're now the one who has to do the training it's going to be done YOUR way.