I have read about the Sansevieria trifasciata, commonly called "snake plant", in Wikipedia (which doesn't suggest any specific snake repellent property).
However, this link suggests that the snakes don't like the appearance of S. trifasciata and they will start avoiding it the moment you plant it in your garden.
How can this plant be helpful, and to what point can we can rely on a plant to keep snakes away? Are there other plants that repel snakes?