I'm building a sandbox for my three-year old. It will probably sit on the deck, so it needs some kind of bottom. Ideally, we should be able to move the sandbox around the deck. Is it necessary for water to drain out of the sandbox, or will the sand absorb enough water? What should I use for bottom?
Landscape fabric: allows water to drain through, but may not be strong enough to move.
Regular plywood: allows movement, but may rot and does not drain.
Redwood plywood: I don't know anything about, but I saw it at Home Depot, and it may be more resistant to rot.
Edit: Combination: plywood with a few drilled holes, covered by landscape fabric.