How can I keep snakes out of my yard?

Get a couple of barn cats.

Moth Balls! They work. Put them around the edge of your yard and the snakes will not cross the line.

Okay, so why don't you want snakes in your yard, are they venomous? Cats and dogs both are good for deterring the snakes. But that isn't the solution if they are venomous. If they aren't venomous they are helping keep other pests from your garden. They'll take care of mice, voles, gophers and other critters like that. Think about them as being an asset not a liability. They are more afraid of you than you are of them.

I was going to say moth balls too but keep in mind snakes can crawl under and around a lot of stuff so it might not be as effective as you would like

To get rid of Reptiles, you have to get rid of their needs? (Food/vermin/birds, Cover, Heat/cooling, water/moisture)

What kind of snakes are they?