I personally like an oil and wax finsih. It may not provide quite the protection that a varnish does, but with a little care I think it can do the job. Think about a gun stock. They exposed to a lot of elements and keep on ticking. And they usually only have an oil and wax finish. I think a call is the same way. Just add a little oil to the calls, on a regular basis, and I think the call is good to go.