My dog got good at killing them too. It was cute, she would suddenly notice a spot in the garden, and look with her head cocked, then suddenly she would pounce and stick her nose in the dirt, then all of a sudden she emerged with a fat vole in her mouth. She was raised hearing "get out of the garden", and is really good about staying out of the beds, so when she was hunting I just went with it- she didn't do any damage compared to the voles.
