How are you using the rubber bands? I toothpicked mine and it just tore itself free after 2 days. The Xenia on the other hand attached in like 8 hours lol
I have fragged my colt coral several times as well, I have found that the best method is to take a needle and some thicker thread and attach it to a piece of reef rubble. i run the threaded needle through the base of the cutting, go around the rock and tie it off, it must be snug enough for the coral to be touching the rock but not to tight or it will rip out, place in a low flow area, within a week it should be attached.
then you can cut the thread and pull it through the cutting.
I have done this with colt and xenia. works very well for both.
then off to the LFS to make some money