If you plant Hellebores, Monkshoods, and daffodils around them, all of those are poisonous, and the voles may not want to tunnel through those roots to get at your peonies.

Some cats are also quite good at catching voles.

I was gonna sugest getting a cat too. We had a small cat colony (maybe 5 total) living in my back yard till this winter when my hearless wife trapped all of them and sent them away. I'm now starting to see more chipmunks, rabbits and other animals that screw with my garden.

I have 5 Peonies and 3 of them bloomed great this year, the other 2 didn't again for the 3rd year now. I forget what they even look like.