We have had an ongoing battle with chipmunks over the years. They dig under my porch, my driveway and in the lawn! For some reason, this year has seen a big decline in population. Coincidentally, we have had a family or two of Garter snakes take up residence. Sure enough, according to several websites, they do eat chipmunks. I guess these snakes have to get them as babies as they are pretty small compared to a grown chipmunk.
We were fine with chipmunks around until they started digging under the porch. Every year ever since we would find mice, snakes and even chipmunks in our finished basement. We've been trapping them with sticky traps but was starting to be a nuisance every year usually around fall. We fixed the problem by replacing the clay soil under the porch with crushed coarse gravel. Once this material settles and hardens chipmunks are unable to dig through. What a relief. Haven't had a rodent in the basement in three years now.