I'm also very sorry for your loss. Neighbors that don't contain there animals are a real pain. My neighbor hat a huge pit bull and doberman pinscher. And they break lose all the time. I'm always telling my girlfriend get my shotgun. Iv always had success with just shooting it in the ground. But I don't trust that one day they will go after my free Rangers. I now have a 4 month old German Shepard already 48 pounds. That patrols the yard and is very protective of her chicken buddy's. They leave there dogs chained up all day and night. And I just think when they get loose there looking for trouble to get into. So I prey I don't have problems with them one day. The sad part is I live on 8 acres and they still get in my yard from time to time.
Get a paintball gun and freeze the balls. Some will rupture but some will not and fire a mix of frozen and non frozen ammo at them. the frozen ones hit hard and the non-frozen ones splat and scare the dog because he thinks he has been injured. I don't know if it scare the bejesus out of the dog or the owner but every dog I have shot with one has not returned.