Anytime you leave your flock roam, you are risking their lives to several predators. If its not your uncles dog, it will be someone else's. Dogs can sniff pretty far away. Chicken poop is a very easy scent. Plus, there will be hawks, eagles, and whatever else going after your chickens.
We spent a fortune on our run. We have welded wire along with hardware cloth. We roofed the run with steel panels to match our house.
Our coop(12x4x9) is a room built inside our garage. It's too hot to leave them inside, so I also free range.
I've steered dogs 5 times in the last year out of my yard. I have pepper spray and a stick. I've had hawks swoop 2 times in the last 2 months. Eventually something is going to get them at some time. We are building a fence starting next spring to keep the dogs out. Eventually, we will have our 4 acre lot fenced to keep the dogs running at large out.
The dog should of never been brought to a coop. Beating the living daylight out of dog is cruel. I would of called animal control family or not. The dog will be back. I see the same 2 dogs back in my yard after my flock.
Your uncle did repay you and that is good. I'd be going out and replacing the ones lost.
Good luck.