I imagine the right answer will be very heavily location dependent, and my local ecosystem is very different from yours but for what it's worth:
We just couldn't find anything that worked until we setup a flexible electric fence around the outside of the run. We lost birds to bobcats, hawks, and mysteries never made clear but I know we have fox and bear and coyotes.
My coop is super tight - no holes in the floor or corners, all windows covered with stapled hardware cloth. I have a Pull-et Shut automatic door that is not a weak spot. The run is chain link fence 6' high that is dug 18" into the ground to prevent tunneling predators and the ground level parts are reinforced with hardware cloth. Nevertheless I have chased a bobcat out of the run, they can leap to enormous heights. That's when we setup the electric fence in a loose large "paddock" outside the run, and that has been the solution for us. Even predators that can leap a fence with ease will typically creep up to see if it's worth the efforts, and since they lead with a wet nose they get a nasty surprise and run away. The fence can be baited with a strip of bacon or similar to invite them to learn the lesson.
I have also chased a hawk out of the run, he had landed and was stalking my terrified hens - a maypole type setup with a few ribbons has worked very well, makes them decide that they would have difficulty taking off again and they don't fly in. The birds sheltered instinctively under their coop and didn't come out for nearly an hour.
I have not had difficulty with snakes or raccoons but my neighbor has had a few massacres as they can reach through anything bigger than hardware cloth and tear a leg or a wing off a bird.
We are moving the coop to a new spot and intend to build their new run out of welded wire with 2"x4" openings and an actual roof. To save on the effort of digging the fence down into the ground we will lay it out across the ground extending 18" in all directions to frustrate diggers such as a fox or coyote.
