LOL this seems to be a really common question, so I might make a thread on it. xD
You can buy sponges to cover your inflow, or block your outflow with a sponge. You could even purchase some drifter plants (preferably silk so they don't blow all over the place). Don't use a sponge that you wash stuff with. This is a different type of sponge. If you're going to PetSmart, then I would suggest Fluval's. Of course, you'll have to cut it to size. It just slides right over the intake. I'd start with that and see where it goes from there.