A good easy way of keeping snakes away from your yard or other areas is to use some ammonia since snakes hate the smell of ammonia and will stay away from any area where they can smell ammonia coming from.
You can soak some old rags in some ammonia and place the rags in the areas that you want to keep snakes away from and you should have no more problems with snakes.
You will have to re soak the rags again every week or so with ammonia to keep the ammonia smell fresh on the rags.
You should place the ammonia soaked rags in unsealed plastic bags to help keep the rain and stuff off the rags and place them wherever the snakes are hanging out at.
Also make sure to keep any debris such as weeds, wood piles etc out of your yard because snakes like those things and will hide in wood piles, weeds etc.
You can also buy some Ortho Snake B Gone and sprinkle it around where the snakes are or plant some lemongrass since snakes also hate lemongrass.