Well first, let's talk about voles and moles. They are very different creatures with different feeding habits so I'm not sure which one you have here so I'll talk about both. Moles are carnivores that make tunnels across your lawn. They mainly eat earthworms so during the spring, when the weather is cool and moist the earthworms are near the surface of the soil and that's why the moles dig their tunnels. As the summer heats up, the worms go deeper into the soil and the moles follow. Liquid Fence has two very good products on the market now to combat them. They have a liquid spray and an imitation earthworm repellent you place in the mole runs. It does not kill the moles, but they eat the ""earthworm"" and leave the location because of how they taste. You should be able to find both products at stores such as Lowe's or Home Depot.
Now voles are actually a form of field mice that are vegetarians. They eat plant material and are mostly a pest in the winter when they can strip the bark from young trees. To combat them, the best strategy is to use standard mouse traps baited with peanut butter.