Nighbours tease my dog- how can i stop this?

You really need to talk to them or the police dept as this can be a dangerous situation.I had a Border Collie that the newsboy use to tease and this was the sweetest dog to my kids and everyone else till this happened.He was on a long leash in my yard that was unfenced and I was wondering why he was getting mean.Then one day I looked out and saw the newsboy hitting my dog with the paper.My dog broke loose and chased him up a tree but from that day on he was mean to other people.I would have to put him in another room when company came over but to us he was as sweeet as could be.I say confront them and if they don't stop talk to the police as this dog can be made mean..