We keep our sand boas on "sani-chip" which is a form of aspen that is chipped instead of shaved or shredded. It acts very similar to crushed walnut shell and is very easy to spot clean. Another advantage is that it is a lot lighter than sand, and does not scratch or wear down the racks we keep our boas in.
I've never seen any problems with impaction either, or if there was a problem it sorted itself out before it became a noticeable problem (if you know what i mean).