I don't have voles, but when I had a mole infestation, after trying a lot of things I just went out each morning and stuck the hose down the holes and flooded all their tunnels as best I could. Especially in spring when they are "denning" underground, they will move away fast if you flood their dens and that will prevent a whole new generation of young ones from making a home in your garden. It took about 10 days for me to see no new tunnels doing this.
If you try this, and it works short term, then put out the scent deterrent to prevent them coming back, that might be an excellent solution.
