Well, I have a low iron glass tank so he won't work.Its funny until he drags a piece of rock across your glass and scratches it like they did mine, thats why I ultimately removed them. just make sure you have enough room between rock and glass to fit an urchin carrying more rock.
they keep moving and squeeze into places, absolute bulls! Seriously consider your situation too, if you superglue frags like me good luck they made me re glue everything multiple times...I have 2 pincushions you can have if you want them anyone for sure local can