All the debris stays on the top. If you're axie hasn't trampled over the poop, you could just scoop it with a turkey baster. If he trampled it all over the place, you can lightly gravel vac over the sand. As long as you don't stick the gravel vac straight into the sand it will just fall right back down. Poke around the sand occasionally if you add more than 1/2 an inch.