For some of my larger island.... I drilled some holes and then used some heavy duty black zip ties. These things are extremely strong. I then used a two-part beige colored epoxy. Probably the same stuff as you used...but different color. I then let it cure for a couple of days before attempting to move anything. The smaller island is dry stacked. I wanted some flexibility to rearrange that side of the tank. Of course... now the corals have fused some of the pieces after three years.