My first coop I enclosed an existing horse shelter. I used plywood around the 4x4 structure. I had a chain link fence around my yard, then chicken wire yard around the house. Dogs came in yard almost every night once I got the chickens in the house. I put rocks and wire around the chain link, they just pushed and dug in another spot. They dug into the house, I put a cement floor. The cement and locking them up every night helped, but then they came in the daytime!
Now that I have learned about electric fencing, that is what I am using the next coop. I was at a Bed and Breakfast on Widby Island and they had chickens. I was worried, because I had a Brittany, and she wanted those chickens. The owner said, "Go ahead and let her run, she won't get the chickens." When I let the dog loose, she made a beeline for that chicken run. When the nose made contact, what a show! A mid-air U-Turn. She would not even look in the direction of those chickens, all week. She was not harmed, but she learned she did not want those chickens!
You can have a lighter built hen house if you use electric fence. It is worth the cost, I think.