Fishing line, black cotton thread, rubber bands, super glue..all great ways to keep the java moss in contact with the wood until it can form its rooting structure & attach itself. Rocks & harder woods (mopani especially) will take longer for the moss to attach. Don't worry about it clogging your filters. You would have to neglect your filters for a while to get enough in there to actually clog them. I make all kinds of crazy stuff out of moss--fake trees, floating "lawn" squares, moss walls, etc...