You can put it on the rocks, but I'd recommend you put it in the sand. Burry it partially and it would burrow down all the way until only the feathers are showing.
Yes do keep an eye on your dusters. Crabs will definatley nip them, seen this with my own eyes and now my first feather duster is growing back a new crown due to this.
My camel back shrimp also found a taste for them too. Because I love my feather dusters I no longer keep any crabs or shrimp only snails.
Does anyone know if dusters touch each other does this cause any harm?
I wouldnt think it would hurt each other "they dont hurt me" When I move them "do to falling" I brush there crown with my finger to make them go in and move them. They dont sting or anything so touching wouldnt be a problem. Also my crabs are really sweet to them "my sally lightfoot crabs are kinda roof ut there trying to role them to get the parasites off them its kinda funny to watch" Also to the main question this is where I put my feather dusters at.
This is my hawaiian it is on the bottom of the tank inside of a barnacle and it comes right out the hole.
And this is my dwarf colored orang feather duster. I like this one the most but the hawaiian is bigger.
He pokes right of my this cave and looks like some sort of tall polyp coral sorta thing lol.