you can do a number of things....
#1 you can let it roll around the tank...it will possibly attach to a rock
#2 you can get a tupperware and get pannyhose or bridal material or mesh(plastic not metal) and rubberband that to the top of the open tupperware
and leave either sand or lr rubble in the bottom of the tupperware and eventually it will attack to sand which u can superglue to a rock or lr rubble where you can place somewhere....
well now im out of breath...if u need something just ask