Bark at the dog, it works for me. And if that doesn't work, go ask him or her to please have the dog inside at night.
How do I get the neighbor's dog to shut up? (my neighbor is a cop by the way)
Buy a dog who can bark.
Tell your neighbor. Who gives a crap if he's a cop. Same laws as the rest of us. If he doesn't do anything call the police and file a report. Seriously.