That’s the way I have always done it when using a loop to backing(I don't always use a loop) You just need to be sure that the end loop is large enough for the fly reel to pass through otherwise there is no way to un-loop it. I also use another knot for a 'hard' connection but it's not easy to explain; it's more like a whip. A local guide who worked in a fly shop by the name of Randy Small showed it to me twenty years ago. You put a few inches of backing over the fly line, then wrap back over the tag end about twenty times, then close it like a whip knot by pulling the tag end through the backing a few turns before the end with a seperate small price of backing.