go with java moss . it will grow on anything rock, drift wood, heaters, filter tubes ecx !!! and if they destroy the moss it will grow back in a week. lol.
i have to trim my moss every 2 weeks.
Yeah you have some trouble when its big because there alot stronger they do like to do it and they can move rocks two so you might see bigger rocks move to the other side in your tank i see it before with my own eyes.
i found if you want plants with o"s keep the plants out of there bedding areas and they do great. in their beds they will digg them out and move them. i like to scoot gravel and sand in my o's bed when i clean the tank just to watch him git madd and move it all back like it was he will spit the gravel at the front of the tank at me lmaooooo.
One thing I've found with oscars, if they don't like where you want it, they will move it with total disregard for anything you say or do. You may also risk losing a finger if you try to argue your point. They are not fond of anything that they don't find to be to their liking, and they really don't care how you feel about it. I found it out the hard way, I kept putting a plant back in a corner, they didn't like it, they moved it, I'd move it back. Well, they each took a peice and ripped it apart.......as to say, now whatcha gonna do?
Notice the air stone, they love to sit over it. All of the plants are on opposite sides of the tank from where I put them. And you can see how the one plant is in different peices, that was their temper tantrum.
I have given up, and let them do the interior decorating.......