I'm with Silver Creek: I've had a tough time finding the right joint for nylon to fluoro. Tried the blood, surgeon's, loop-to-loop, etc. Tried the rings, which seemed like the ideal solution since the two materials never touched, but had several rings open up on me. I think for stream fish they would work, but on big lake rainbows & browns I quit using them.
Finally settled on the Orvis Tippet Knot (Google it). I tie 2X leaders to 4X fluoro and never have a problem. It's a tricky knot to tie with clumsy fingers (I made a little tool out of a paper clip that helps), but easy to get it right and no pulling on the tag ends is required. When that knot breaks on me, I know it's time to 86 the leader and spring for a new one.