Snake problems can be addressed in a couple of ways. The first is habitat control. This can be as simple as moving yard junk, brush, or a woodpile. Keeping rough areas cut short is a big deterrent as it removes hiding places. Another means of control for snakes is to make the area inhospitable to them, with repellents.
Snakes use their tongues to test their environment, much the same as other animals use their nose.
The flickering tongue collects molecules of the area and brings it in to the Jacobson organ, which determines if the area is hospitable or not, or if something is food or not. At first I tried barriers of lime and had no success. Having never used the product, I explained to the customer that it was a new trial product and that I could not offer any guarantee. This customer has a big snake problem with black rat snakes around his foundation and flagstone retaining walls. With nothing to lose, he agreed.