Snakes in my wall

Question:
I have a place at a local lake. It has a 40 foot loose rock seawall. Some water snakes have taken up living in the rocks. It is disconcerting, if not dangerous, to swimming children.
Is there an environmentally friendly method, such as moth balls or other products, which might convince the snakes to leave?

Answer:
Thankfully yes. There are some great, safe products available now that will make almost all critters go away without harming them or causing any nasty side effects. We use small containers that allow the repellents to work over a long period of time with no environmental converns.