Acrylic rods and epoxy -
https://www.bigreefdepot.com/Aquariu...ocks-s/125.htm
There's always a chance glues/epoxy's/cements etc won't hold or will crack, decreasing the stability of your rockwork. Drilling the rock and using acrylic rods is a definite way to prevent avalanches and potentially glass shattering rock crashes.
That being said, Eli know's his stuff with fijicrete, after all, he is the rock guy!