I also agree for rockwork to use zip ties and rods. I also use Super T and the epoxy sticks to firm up and help support the structure. I found that using each glue individually does not provide a strong hold but using them together provides and lot stronger hold. I also use this method for all my frags or placing new corals. It works best if the pieces being glues are dried off first.
Basically you kneed the epoxy together.
Dry off the spots where you want to glue.
Place a generous amount of the Super T on one end.
Put a piece of epoxy over the Super T glue.
Place some more Super T over the epoxy and then put the two pieces together, hold it for a couple of seconds and you are good to go.
While placing a frag underwater you must hold the frag for a little longer. I put a lot more Super T on it than I would if it were dry as it starts to set as soon as it hits the water.
I stay away from the purple coloured epoxy's as it seems to slime up as soon as it hits the water and it takes longer to cure in my experience.
I use the 2 oz Super T Cyanoacrylate from Lee Valley.
http://www.leevalley.com/wood/page.a...at=1,110,42966
I don't want to experiment with the non reef epoxy's so I stick with the Holdfast epoxy.
Hope this helps a little.
Dave