Re: Backing to fly line question?
+1 for Zap-A-Gap. Assuming your are using a nail or Albright knot that is well tied (depending on the fly line core material), coat it with a droplet of the gap filling super adhesive and whick off any excess. Allow thorough curing time, about a 1/2 hour and you are unbreakable. You might also have a gander at the earlier "Welded" Loops thread in this fly line forum.