I have never tried glue before but I've heard that it's difficult cos they slime a lot. What I have had success with is to tie the frag down using cotton thread, not too tight until the flesh is pinched but tight enough to stop it from coming loose due to the current. It will attach itself on the surface after awhile. Mine took 1-2 wks to affix before I cut off the thread.
some pple also use rubber band, netting, stocking, etc & let the frag attach itself.