Urgent! How do I keep my 4 chooks in suburbia safe from a nearby snake?

[Shell from Zim]

My birds kill snakes, and they are just bantams... well they alarm call very loudly first so it's pretty hard to ignore them. It frustrates me because the poor harmless ones will get taken out too. Snakes are wonderful to have in the garden to control the vermin... and very few are actually venomous or harmful. I hope you find a comfy balance.