If you want to lock the loop in position more firmly, then take one
side of the loop once or twice around the hook shank, before feeding
the loop over it.

If you get a big fish on the dry, this will kink your line more as it
slides down the leader, but this did not cause me any particular
problems. The biggest problem I had was actually getting the loop
through the eye of some smaller dry flies, which is why I prefer the
leader ring setup as well.

You can also lock the leader ring more firmly using a similar
technique, just thread the loop twice through the ring, before
threading your fly and dropper through the loop. This will still slide
easily if you loosen the loop, but will take a lot more force to slide
it if the loop is tight. Indeed, if you feed it through three times
for instance, it probably wont slide at all unless you loosen the
loop.

I broke wet 6 lb mono trying variations of this, without the ring
sliding at all of course.

However, if I was getting a lot of fish on the dry fly, I would take
the nymph off, and fish a pure dry fly set up anyway.

TL
MC