We have discovered many mounds in our lawn which apparently are related to voles. What is best way to get rid of these critters?

There is a product called "Mole-stop" available at Lawn/Garden stores that you sray onto your lawn with a hose end sprayer. It has some essential oils and eugenol in it and apparently acts as a repellant for moles, voles, and chipmonks. I heard about this from a Groundskeeper at a PGA course several years ago and it seems to work.