So sorry. Some people are just not very responsible for their animals. I had to threaten a neighbor once, after talking to them many times, that if I saw the dogs loose again on my property I would have no choice but to shoot them. In that case, that took care of it. Sadly, some people would get really upset if something happened to their dog, but are numb to the pain their dog might have caused someone else. Do you have animal control where you live, that can address the owners? Rules, laws and enforcement can vary a lot place to place, best to know what options you have or don't have. If nothing else, you can make the threat, if it's legal to shoot to protect livestock where you are. Why people do not secure their dogs, I will never understand. If it were an "accident" there would not be multiple victims. If it's loose again, it will likely return to the places where it had so much "fun".
The only thing you can really control is the security of your flock. If possible I'd try to provide them with a place that dogs can't get into easily. I spent a lot making my enclosure secure from stray dogs. We get them a lot, I pick them up on game camera's going through my property at night pretty often. If they get in my pasture my donkey will take care of them, my house dogs (big un's) take care of around the house, my birds are behind a 7' fence.