Did you know that koalas' brains are so small and smooth that they basically can't learn? Zoos couldn't keep them alive for the longest time because nobody figured out that koalas cannot process that something is food unless it's still attached to the tree. They'll starve to death before figuring out how to eat out of a bowl. They'll also refuse to eat eucalyptus leaves from anywhere outside a small area around where they grew up.
For the snake, I'd clear away any brush and plants you can from the paths and chicken areas, and use small-spaced hardware cloth around your chicken areas. That's basic snake-prevention protocol.