Mine only go in the rocks if they are scared, if it is a male being harassed, or a holding female. They are in a 55, decorated just as GTZ described, and the males are about 4 inches long. They are very peaceful except for spawning time, when the dominant male picks out another single male he particularly dislikes, and pretty much sticks to chasing him and him alone. This wouldn't be as bad if I had a better male/female ratio, which is currently 3:3. It used to be 4:3, but I had to remove one male due to pretty extreme harassment from the dominant male. In the last round of spawning, which was with only three males, the singled out male got pretty stressed, but I am honestly not sure why, as there was minimal aggression. They are a great fish, I have enjoyed my group, and have raised some of their fry, which have grown faster that I expected, being an inch long at less that three months old. Good luck!
P.S. My tank is decorated with come hollow ceramic rocks I picked some up at ACA 2010, and they have been useful hiding places for the unfortunate male to hide in during spawning time.