re: Think a coon is getting after my chickens

If the head is gone it’s almost certainly a mink.
Possums usually only eat the guts. They do eat eggs and feed, though.
A coon will eat almost the whole thing.

Best recourse is secure the coop like mentioned, use hardware cloth to seal all gaps, trench filled with concrete with the wire in the concrete is best. A mink can go through a tiny hole.
Automatic door is a lifesaver. It will save them if you are late getting home to close the door.