I have never had anything (knock on wood) get into my coop, it is like fort Knox
but my neighbors across the street have had three flocks of chickens and every one has been killed. We have skunks ( yes I have been sprayed) and raccoons all over! Their coop and run are all together so at night they can not just close the door and lock them in. The skunks and raccoons dig under, open doors and get in anyway they can to kill their chickens. (after three flocks you think they would do something better) the raccoons climb the trees and get on top and pry open the chicken wire where it is not secure to get in. Very sad....
I buried metal around the door of my coop, and the coop sits on buried cinder blocks for added protection, the windows are covered in chicken wire and closed at night. I also have a rooster that stands 8 ' tall ( ok maybe not 8) I think would scare off any preditor!