The advice I give to people who have received xenia frags from me is to be sure that there is nothing of importance (ie. other corals) on any rocks above where they put the xenia frag because once the xenia takes hold, it will quickly spread up anything (rocks or otherwise, including the sides of the tank) in its way. A year ago I received a single stalk of xenia. It now covers the entire right side of my tank. The only coral that I have seen hold its own against xenia is GSP. I have has SPS frags knocked into the xenia bed ("weed bed") by my fish and/or snails and the SPS is dead within a day.
As to fragging, what works best for me is to cut the xenia stalk off even with the rock and then stick a toothpick through the bottom of the stalk - you then can wedge the toothpick in a hole in your liverock - the xenia will attach in as little as a week if it likes your tank lighting and water parameters.