You can put the feather duster in the CC, or you can put it in a hole or crack in your rockwork. It will eventually attach itself to the rock. Different anenomes prefer different conditions, so it may decide it wants to be on the rocks instead, but if it is healthy, it will move around on its own until it finds a place it is happy. The only real reason to try to find a place you think it will like to stay is that then, if it DOES like it, you will have chosen a spot where it is convenient to have the anenome. It can be really frustrating when they decide they want to be at the back of the tank where you can't see or feed them. Once they attach to a rock, it is very hard to remove them without damaging them.