Garter snakes, like most snakes, cannot dig holes. If there are holes created by rodents, for instance, they will often take advantage and hide there. There are two simple things you can do to keep the snakes away. The first is to keep the grass mowed short around your house and patio. Snakes prefer deep grass and other structures that allow them to move while remaining hidden. They are less likely to cross short grass.
The second thing is to prevent rodents from burrowing around your house. Thirteen-lined ground squirrels, chipmunks, pocket gophers, and voles are known for their hole-making ability. If they dig holes anywhere near your house, snakes may take the opportunity to hang out in those holes. So, prevent rodents, and you will discourage snakes. Remember also that snakes are beneficial animals, as they eat small rodents, such as mice and many insects.
Avoid using snake repellents. The evidence for their effectiveness has not been thoroughly documented.
Online Resources:
Reptile Management
