I have a group of 3 varying in size, no rogue activities. When I only had one I always sorta suspected it of causing trouble when I wasn't looking.I've heard from more than one source that if they are kept in a group, they are less likely to go rogue. Not sure why, but I have three people with emeralds in sps/lps filled tanks that have been in there for years in groups of 2-3.