I suggest going to petco or some other pet store and pick up some direct stop. It is a totally safe citronella spray. It works great for stopping aggressive dogs in their tracks. I have used it in the past and my wife who works at a dog daycare uses it for those trouble dogs that come for a trial day and start fights. It keeps everyone from getting hurt and gives you enough time to remedy the situation. This is not a cure for this dog. They cure is call you local city hall and ask about off leash laws and put in a complaint of an off leash and aggressive dog. Keep calling until it is resolved. This dog does not sound like he wants to play. Most dogs owners don't understand dog behavior and often mistake aggressive behaviors has I wanna play. There are clear differences, also alot of dog owners with dogs like that ignore it because they won't admit their dog has aggression issues. I would also try to talk with your neighbor one on one. It will be their worst day ever when this dog bites, has to be put down and they are sued for medical or vet bills. Good luck. If you have any questions pm. If I don't have a direct answer I can talk to my wife. She has several years in dog behavior.