Voles are poor climbers and not very persistent diggers, so it's possible to keep them away from your hostas with collars of 1/4-inch hardware cloth that are buried 5-6 inches into the soil and extending 5-6 inches above the soil. They also are deterred by digging in rocky soil. You can buy a sharp gravel or perlite product (one brand is called Vole-Bloc) to dig into the soil around the plants or work it into the soil when building a flower bed.
Another option is to trap them like mice. Baits made of equal parts peanut butter and oatmeal work well.
There are spray-on repellents that contain castor oil and other smelly compounds, but you'll have to apply them repeatedly.
I have used more than one approach, and was persistent--over time, the population of voles (and the amount of damage) did diminish.