That's a really good idea too! Thank you!Get a one of those plastic storage boxes with lid at Wal-Mart. Not the hard, clear kind, the solid color ones. Red and green ones are sold after Christmas, other colors throughout the year. You can choose the size you want.
Take a knife and cut the bottom out. Set it where you want it, wiggle it into the ground a bit (so you don't lose sand). Fill halfway with sand. Cover with lid to keep rain out.
I put one like this in the run (without the lid). It's too small for my full size hens to use as a dust bath. They like to snuggle together inside it on windy days for a nap.