I was just thinking. I've tried that tight wire mesh that's used in new construction for stucco application. Works ok but sourcing is an issue.

I was thinking , why not plant your plants in old metal colanders or steamer pans..the perforated type. You can find gobs of them at garage sales and flea markets. The holes are small enough to keep the voles out but large enough for feeder roots to exit the enclosure, some made wider if necessary. The aluminum ones wouldn't transmit much in the way of sun/heat and they wouldn't rust. If they have handles (especially commercial(restaurant)steamer baskets..you could plant something you need to bring indoors for the winter by simply loosening the soil around the basket and lifting the whole thing into a temp planter. Hmmm..might try that.

Might be wrong but what if I'm right and it saves an important plant?

Since I have a new cat, the vole population has all but disappeared. He's decided they aren't worth eating but they're good for about an hours worth of harassing before killing them.