on slate, i use a small brillow pad, most calls you buy come with this. and i lightly re-surface the call in order to get it opperable again. i also use a light grit sand paper to re-condition strikers, i hold the striker in my fingers, and at an angle i brush the sand paper against the tip while rotating the striker.
i do this same process every time i sit down! it is necessary to get a good sound out of the call!