You can either go down the legal route and involve the police, as i did years ago with my boyfriends neighbour, who spied on us that much he actually commented on which underwear i was wearing.
Or you could hae a bit of fun with him, make up some signs telling him where to get off, ask him where he got his binoculars from as you need some to spy on a nosey neighbour, or for the ultimate fun get your partner to act out a fight , pretend to hit them really hard knocking them out, see if he phones anyone, and if they come act normally, but tell the police that he is always spying on you and making up stories, hes sure to end up in trouble with the police.