They naturally roll around is how they grow. They can handle a wide range of water conditions. But I seen them die and turn white in LFS tanks that wasn't giving them good lighting. If you tie them down it might cause the bottom side that wont get any light to turn white. If you kinda lock it into a spot with rocks or wood it be good to once in awhile rotate them so the underside can get some light. But they can float up out of that spot if they want to. I had a giant one about the size of a Grape Fruit. It got torn apart by my Dovii. since it now is ripped open I lay it kinda over some driftwood so its not a ball anymore and stays in one spot. There is plenty of info on them just google Japanese Moss balls.