Last year voles ate all my potatoes. I had some luck trapping them, but not enough to save the crop. Before I plant tasty treats for them again I want to construct beds that will keep them out-- a tall order, I know. I'm thinking of putting up cinder block walls and either hardware cloth or gravel on the bottom before filling with soil. Does anyone have experience with an arrangement like this? Would the cinder blocks (or retaining wall blocks, or anything of the sort) or hardware cloth pose any sort of chemical problems in the soil? Would they be effective?