with most soft corals such as star polyps and leathers, you can simply cut pieces off and attatch them to other rocks and they will usualy grow into new specimens. xenia grows by fraggin itself, so if you have a rock near it it will grow over the rock and youcan then cut the attatched stalk from the main colony and voila!. with hard corals sps, for example can just be broken off and glued to another rock where they will eventually grow into a new colony, and with lps like candy cane and cup corals, you usually have to wait until the parent colony grows a new polyp stalk , and then cut this piecs off near the bas and glue it to another rocka dn bada bing, youve got lots of frags!
good luck
jon