I taught my dogs the "enough" command. Both mine know how to speak on command so I would say "speak" then "enough" and treat when they stopped barking. Is there any sounds that could be triggering it? Trash truck? People? a dog? My dogs started barking every night and it turned out to be a family of foxes running through my yard every night. They started it up again and now there is a loose GSD in town that no one can catch. So there could be things triggering it.