Thanks for all the responses.
The neighbors have not called looking for their dog. I have not approached them-yet.
This has been an ongoing situation since I moved here, ten years ago. This particular neighbor gets dogs and doesn't take care of them. Every neighbor in a two-mile radius has had an issue, or two or five with one of their dogs. Sometimes they get one at a time, sometimes a litter. The ending is always the same. The dog(s) get shot, hauled off by AC or rehomed.
My plan is to secure my fence. I am going to speak with my neighbor (the open side) and see how he wants to do it. He will need access to my yard at times and it will need to be something that isn't permanent but secure but we will work something out and get it done. I may end up installing two gates. I have a 4 ft'er and a 5 ft'er. Those could be secured when closed and also able to be opened for him to mow, maintenance his drainage, or garden tilling-and of course, socialization.
As far as the dog owners, I'm not going to bring it up unless I am asked. I had warned them I would shoot her or call AC, so they may know what happened. If they ask, I will be direct and let them know exactly what happened and how fortunate they are that I'm not asking for reimbursement. Next time, I won't be this nice. I am also going to ask them to not own another dog because I really can't afford it.