I am glad I don't have a black snake problem. I don't pen up my chickens but rather let them free range but I do put up nest/laying boxes. I would hate to have a big "chicken" snake laying in one of them as I would be tempted to kill it for sure after sticking my face in the box checking for eggs.
I have heard that if you have several laying boxes, just put a hole between each box and put some fake eggs in each box, the snake will eat the "unbreakable" egg from one nest box then crawl thru the hole to the next box where he will eat another "egg" at which time he will have an egg in him on each side of the wooden plank. You will then have him trapped. You could then force the eggs back up and out of the snake and remove the snake if you so desired.