No, because it is small pieces and I don't put more than a few cups' worth in a big hole for a rose, for example.
I mix it deep in the root zone rather than as a top dressing. How deep do voles burrow? Do they have tunnels or do they stay near the surface like rabbits? Seems to me the sharp edges of the shale would also foil slugs.
I need to do some more reading on this.