I used 3M super glue gel under water.
You have to clean the two surface else the gel won't stick too. Use a screw driver to scrap the surface of the LR slightly.
Once your apply it onto the frag and you put it into the water a layer will be formed.
Next you take the frag out of the water again poke and break the layer and apply more gel.
Then position and press the frag onto the LR, twist it a little and hold it there for a min.
After that apply an additional layer of epoxy around it. This method works very well for me even with colony that is stick to the side of the rock works.