You could also use some loose cotton or wrap the rock in plastic mesh if you have any.so -that- is how you keep them in place. i "lost" a morph that went off floating around the system because it let go of the rock and i just couldn't get it to stay in place.
I tried the rubble in the cup thing. I tried everything but rubber bands!! I have heard that you can sew them through with needle and thread (through the foot) and tie it on that way.You could also use some loose cotton or wrap the rock in plastic mesh if you have any.
I used to put some rubble inside those cheap plastic shot cups and then put a morph in the cup in low flow until it attached.
This is the second time i have sliced this guy in four... bounces back just fine....Good chance youll kill them and slice them in half doing this method. Never do this method for rics or morphs... just place them in pvc pipe with rubble with netting across and leave in low flow area to attach.. or leave them in a breeder box..