Fox, Coon, Coyote, Wiesel, and the old Nasty Possums, are just some that will reek havoc a chicken population, don?t forget chicken snakes, they will not only eat eggs but baby chicks as well, even the common house cat will decimate a baby chicken population, Hawks and Owls as well. Another great enemy is the bobcat. They will come back night after night hitting fast, and gone. (Sometimes in broad open daylight as the rest will do as well, but most of these seem to prefer the safety of darkness excluding hawks of course).
As you say Reagan a good yard dog will cut down losses tremendously. At one time we had a German Shepard that proved to be a real family friend as well as a friend to the chicken flock. He would put a bobcat up a tree as good as any coon dog after a coon. With (Boots) around the chicken flock was in good paws.
Phillip