 Oh my gosh, you can put all kinds of marks in the concrete that's very difficult to get out sometimes. But the trick when you're washing around a pool is to not get all of the debris into the people's pool, right? So we use a surface cleaner that basically keeps all that debris very low to the ground so it doesn't go into the pool. Now, obviously I can't keep 100% of it out, but your pool cleaner will clean up once we've left.