If you have any debris around your yard such as wood piles, rock piles etc around your property clean up and/or get rid of the debris where the snakes like to hide.
Trim back heavy brush or hedges where snakes can hide also and seal any entry points into your house.
You can also soak cotton balls with cinnamon or clove oil and place the cotton balls around the areas where the snakes are to keep the snakes away.
You can also do the same with strips of fabric soaked in cinnamon or clove oil.
Contrary to popular belief moth balls and egg shells will not deter snakes.