Lovely rics. Is the urchin crawling directly on them in that pic?
Does the urchin cause any problems? Knocking things over etc?
the urchin is on the window.
urchin's are very usefull in "preventive" controlling nuisance algae.
for this reason i alway glue my frags an corals to the rocks. you can always (re) move them later on. if they fall off the rock usually the damage done is irreversable.
i just let nature take its course....