I prefer wood and of rock in my tank, I think it looks quite authentic. As the Oscars gets bigger, you will realise that keeping any tank mice and tidy will be very difficult. They will be for ever taking in the substrate, leaving great big pits. Given half a chance, they will move any of your ornaments around and have a go at anything that is in the tank, including heaters. You must make sure that you use a robust heaters, my Oscars take great pleasure in rattling the heaters against the side of the tank, if they were cheap rubbish ones, they would have broken them by now.