put out poison bait and seal the entry points. i never had to deal with voles, but from what i understand they are like mice in that they can get thru a small opening, much smaller than you would think.

A hole about the size of a nickel.

Take care of it like you would mice.

Spray foam will only slow them down. We live in the country, nothing we did kept them out. A time happened when I thought spray foam fixed it so I scrubbed and bleached the concrete basement. The next day I went down there to get bread out of the freezer, not only was there mouse poop all over but they had chewed up the spray foam. I knew then I was fighting an army.

I went to the store and bought 50 year warranty (thought it would be harder) door and window caulk. I went around the outside of the house looking for and filling every little gap. I used an entire tube on just where the electric comes into the house.

Knock on wood, this is our second winter without mice in the basement.

We have Voles in our front yard. I like them. They eat the 5 bushes the homeowners association said I had to have. The Voles eat them to the nub every winter but never kill them. I can still plant my flowers in the tiny 12" deep by 10' long space AND the 5 required bushes still show signs of life and grow back to about a foot tall before winter comes again. LOL