No, test n confirm the position you want to place your rocks, get it out from water, dip some bsi gel glue and attached it.
Or these gel glue that copperband recommend, stick fast n very good to use. Sea view selling $2 per stick.
Cheers,
James
http://www.sgreefclub.com/forum/topic/105744-the-journey-to-the-valley-of-the-reef-by-james/'>