Chances are it is a harmless snake. If it does have the yellow ring around its neck it is a ringneck snake. They are not poisonous so you can just pick it up and put him near your compost pile. Odds are whatever you have down there is innocous but without a picture or further details it's hard to help.
How small? What other markings are on the snake? Yellow strips? One yellow ring on its neck?
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