You don't need to remove the old sod, it will decompose and add humus and nutrients to the soil. If your soil is not good, add more, otherwise just rake out the dead grass sprinkle some bone meal over the surface and lay new sod.

If you decide to add soil, again, rake the new soil over the dead grass, add bone meal and lay new sod on top.

I live up in Amber Trails and we have had lots of voles the past couple of winters... this last winter wasn't so bad. What I typically did was overseeded the areas that had the vole damage (trails) and they always fill back in after a month. Theorectically, though, with winter damage the voles only eat the crown and not the root of the grass (frozen in ground) so it should grow back anyways... but overseeding guarentees the deal.

in terms of control if you don't mind the use of poisons on your property poulins carries a product called "gopher doom" which is supposed to work quite well against voles. They also carry a special box that has holes in the sides that are only big enough for voles to get in... so that the pets can't get into the poison.

Good luck.

We had voles demolish half of our sodded yard last year, they'd hide under our deck for the summer and live in the sod in winter. We got a load of topsoil to help out the really badly damaged areas and heavily seeded overtop; the old sod grass grew up through the new soil, and the seeds will took root nicely.

We've been lucky, our voles decided to move out from under the deck and are now under the fence instead, and seem content not to burrow through our yard. They seem to like the sodded areas better than the seeded ones, they haven't touched the re-seeded area at all, though they did get back into another area of the sod. We didn't add anything to the soil as a vole repellant, though I know there is a product at Shelmerdine's that many people have recommended to me.

Best of luck! Hope this helps.