If you have enough open space, the Scarecrow motion-detector sprinkler works great, even in the dark! They're available on Amazon, seems lots of companies are making them now and the prices range from $35 to $90. I have the original one that is now $90 but I've had it for at least 15 years. It still works like a charm. Down side is plant leaves moving in the wind can set it off, so you need to set it up in an open space facing away from your plants.
That being said, I do think you should be getting together with the neighbors and calling for legal help on this. Dogs roaming free just is not a safe situation and irresponsible people simply shouldn't own dogs.
