I use superglue with good results. It took a while to get the technique down. First, I test fit the frag to find a good spot with a much surface contact as possible, noting where the frag touches. next I gob the glue on those areas. then I push the frag on and off of the rock several times to get the glue to stick to both surfaces. after a few times the glue gets gummy and I press it a last time and its as good as a weld. Good luck.