Minks! Sorry for your loss, those are hard buggers to predator proof for! Hole the size of a dime is the smallest they can get through I believe? At least you have all winter to double check/reinforce everything before getting new chicks. Is your dog trained as a guard dog? My bff had two large dogs that were worthless as livestock protection dogs, finally had to get another and specifically train it. Guess not all dogs still have that instinct. 
