Just a comment on the [I]Building A Sandbox[I] in the June '08 issue:
I learned the hard way that uncovered sandboxes in the play area can be cat magnets. For the first box I made a cover from thin plywood which I laid over the box. Later I found that the well-known all-purpose blue tarps worked just as well.
Just spread it and anchor it any way that works for you..
I built the sandbox too, and my kids love it. To cover it, I attached the tarp at one side of the box using screws and washers through the grommets, and then attached the other side of the tarp to a piece of scrap 2x4 that is as wide as the sandbox. To uncover the sandbox, I just roll up the tarp by turning the 2x4 like I'm opening a tin of sardines. To cover, I unroll it and the 2x4 keeps the tarp weighted down against the wind.