crickey... i never had a problem with rocks, but i got a resin log for my tank... unfortunately i didn't think ahead and with my 6inch common plec... i woke up one morning and found that he had got stuck in it!! eventually he began to find it hard to breathe... so we decided we had to do something as he was going to die anyway... so we took the garden secatoors to him, got the log off... then when we put him back in he shot off and stuck to the filter, and refussed to move for like a day... lol... can't blame him. he's now a healthy 8inches, so he's ok... im kind of nervouse of getting rocks for my tank now...