I am not a fan of aquamend either, but it's dirt cheap at the hardware store. What I usually do is have a container of tank water in which I mount everything on rubble/plug and let it cure in that container, that way once it's fully hard, I can transfer it to the main tank and just put it anywhere without worring if the frag comes off. Seems obvious, but it works. That way, you can also avoid the unpleasantness of mounting your frag to an enormous rock and later realize you have to move it.
I also really prefer the acrylocyanate (or whatever it's called) gels. They don't heat up like the two part epoxies do, and they dry pretty fast. again, i like to do this in a container nearby and then just wedge the rubble into my rockwork.