Just a few thoughts and ideas to help protect your critters. I have friends with chickens and they lost the entire stock 4 times. They listened to my suggestions and they still have the 5th stock. This is not 100% but will minimilize the losses.

Raise the chicken coop off the ground. I suggest about 4 maybe 5 feet. Most important, do not build it near any trees or overhangs. Racoons and squirrels can be kept out by keeping the coop out of reach of trees and other overhangs. On all post legs of the coop. Get some galvanized sheet metal and make a wide cone to go around each post leg about 3 - 4 feet up. About 1.5 foot diameter or more should do it. Make sure the cone is opening towards the ground. This prevents them from climbing up the legs, and snakes cannot slither around the cone easily.

At night, ALWAYS lock them up in the coop. Most kills will occur during the night. Whereas you can minimize land born thefts you cannot prevent all airborne threats. Owls were the most common threat with my friend's situation. As long as the coop has wood roofing and wooden window shutters that can be shut, no flying predator could get in.

Make sure the coop is secure by no open spaces larger than 1/4". If a racoon does happen to get to the coop then it's hand may not be able to get through a 1/4" space. Many times my friend's coop wire would look like a crimes scene with feathers and blood all over the place.

Release em at morning and lock em up at night. You can rig a way to raise the gang plank up through a pulley at the roof of the coop after all birds are locked up.

Just a few suggestions which may help keep your chickens losses minimal.