I feel your pain Ben -
I've been diligent and tried just about everything over the years, oil drenching soil, mothballs, perm-til, wire wraps around bulbs, traps, grub deterrent, etc to no avail for any length of time. My yard looks like a runway, for both voles and moles.
One theory I have for my poor result is, I live on 1 acre in the middle of 25+ acres of horse pastureland. I don't buy ornamental plants anymore, but do put in veg garden