So, if your in Missouri, your best vole protection in winter is to let the ground freeze hard on top before adding any winter mulch protection (probably just after Christmas). And then, really the only ones that would need winter protection would be your Trumpet types. Asiatics and Longiflorum Asiatics wouldn't need any winter protection at all.
Your idea with the pool was cute, but even so, chipmunks and gophers and bunnies would be jumping up in there anyway. The only sure way to keep those little critters out is by fencing with chicken wire or better yet, hardware clothe. You can see right through it and it's hardly noticeable when properly installed. It doesn't look bad, if that's what you might think.
