Mine have never tried to get off their rock, and they don't seem to move about much. As far as behavior, mine have "learned" that I feed during the day, so they are out most all the time. They don't seem to care about the lights one way or another, their rock is right out in the middle of my tank where the lights are brightest, and they take no heed of it at all.

I wouldn't try to chisel one off, just find one on a rock you can pick up. The jetties are made of granite boulders, and you would just damage the nem trying to chisel him off. If you get out towards the end of the jetty, you can get down between the boulders and find the nems stuck to smaller rocks that are easy to carry. If you are there when I am, I can show you another place to collect them that is very shallow and fairly easy to get to.

You should join us for the collection trip next year. Lots of fun activities, and we do a night collection on the jetties for peppermint shrimp, molly miller blennies, nems and lots of other good stuff. I will be there, I go every year