You could certainly take cuttings of your plant and grow them in water... but I don't understand why you would want to do that. For one thing, there are (essentially) no nutrients in water, so your plants are eventually going to suffer and fail.
You don't want any leaves submerged in the water -- they will just rot and foul the water. and I don't think there is any advantage to using rocks, it would just be for "looks." Just take some cuttings of your plant stems (I don't think it matters when you have watered, or what angle you cut at), strip off the leaves that would be below the water line, stick the stems in the water, and roots should form where there were leaves. I wouldn't use rooting powder. But then, I wouldn't do this at all, other than to root some stems to make new plants.
