With Oscars it's best to have deep gravel and to sink any decorations (real rock and driftwood suggested) deep into the gravel. You can also purchase driftwood that is anchored into a slate base for just this reason. It keeps the Oscars (and other large cichlids) from rearranging your aquarium for you nearly as much. If you are going to add plants, fake is *highly* suggested and, again, sink them DEEP or wedge them between firmly anchored rocks and wood pieces.
Also, since Oscars don't swim the same range as plecos do... and plecos are more nocturnal and would be out and about when your Oscars would be less active, I see no real reason why you couldn't keep a bristlenose or similar pleco with them as long as it has plenty of hiding places, real driftwood, and you have adequate tank space for it to scoot around the aquarium floor. As long as it's a type that wouldn't grow to be more than 8 inches.
But that's my personal opinion, which doesn't always necessarily jive with the opinions of most hobbyists here. My arguement in this case is that Plecos are highly beneficial for the removal of algae growth and have different swim depths and activity hours than the other species, so it shouldn't cause any of the classic 'overtstock' issues of competing for space and food or acting out aggressively. The only concern should be water quality and as long as you keep on top of that, it shouldn't become and issue.
