Dear All,
In case people are interested, we've put a short tutorial on modelling stacking faults in topas v6 online at:
http://community.dur.ac.uk/john.evans/topas_workshop/tutorial_stacking_faults.htm.
There's also some information on the wiki at:
http://topas.dur.ac.uk/topaswiki/doku.php?id=stacking_faults
Best,
John