I think Orkie's suggestion is the best so far. From the bit of reading I've done, there is no sure fire way to rid yourself of snakes. So called repellents aren't affective and you would just be wasting your money. Orkie's suggestion of making the area uncomfortable for the snakes, such as keeping the grass trimmed low and removing any rocks they can hide under, is the best solution. If I were you, I would make sure that my entire yard were free from any kind of brush, high grasses and areas that snakes would like to hide. One suggestion I read was to have guineas or geese. These birds are natural predators of snakes.

Killing snakes is just not cool. Get rid of the food supply, and they will leave. Maybe try leaving the pond empty for a while until they go away. A fine mesh perimeter also sounds like a good idea, you can even curve it outward and make it decorative.