If you want to get frags of it I would put some plugs right next to it so it can grow on them. I am thinking of the ones that have the magnet on them and attach them where you want it. If you are only wanting to kill it, then the sand idea is good. A thick black piece of acrylic up against it and a rock to hold it in place. Make sure the acrylic is big enough so no light gets down over the top or sides.
