I have a thread showing many pictures of corals growing onto each other in my display. If you are sucessful in this hobby your corals will always grow into each other much quicker than you think. I often place rocks with coral on them onto and inside other corals so they can all grow together. Works good and looks very natural after they grow in. Its fairly easy to predict which coral will win and after a while you learn what they do. Some grow over, some use chemical warefare, and some just turn and avoid contact. I have never seen a healthy sps coral die due to insidental contact with another sps. I have had a few frags get totally grown over but i can always save a piece and plant it somewhere else. However, LPS will slaughter you sps if they are close enough for their sweepers to reach. They can however be kept in the same systems.