The Four Person Beach Mat is impossible to cover with sand. Used in military applications to contain sand and dust when helicopters land and take off, it’s made from two layers of patented, woven polyurethane that filters sand through to the ground as soon as any falls on the mat. Because of the construction, sand passes through only in one direction, so no sand from the beach will work its way up onto the mat. The material also resists dirt and water, and it’s strong enough that you can use outdoor furniture on it, too. Because it doesn’t absorb moisture, it resists mold and mildew. It has metal D-rings on each corner, so you can stake it to the ground. At 10′ X 10′, it’s big enough to use for a day at the beach or even for camping. It’s $99.95 at Hammacher Schlemmer.