You can put the ricordea into a small glass or container (like Gladware) inside the tank. Put some rubble on the bottom of the container, and the rics will likely attach to the rubble. You can either leave the top of the container off completely, or put some kind of netting over the top to keep the rics in.
You could also put the rics onto a rock and wrap netting loosely around the rock, and rubberband the netting in place.
You could use rubberbands, just be careful not to cut into the flesh of the ric. If you have a porous rock where you can stick the ric into a little dip or recession, and then wrap a rubberband around the rock so that it is holding the ric in without cutting into it, that seems to work well.
