I recently saw I show tank at a LFS that made extensive use of Java Moss as ground cover, with spectacular results. It appeared to be a rather low light tank, but was lush and green with Java Moss (among other plants). I was so impressed I bought a couple clumps of the stuff in an attempt to duplicate the effect. So far the best way I've found to keep it in one place is to attach it to something with fishing line until it takes hold. I've got one clump attached to a piece of lava rock. With another clump I'm trying to cultivate a carpet type effect by "sewing" it to a sheet of black plastic window screening with fishing line. I'm hoping it will take hold and creep out all across the screen. It's still very much in the experimental stages, but is already looking nice.