I've been using the Davy knot for about two years. I have had a few failures so I came up with the "improved" Davy knot. All I do is add one extra turn to the last step. No failures now. It has works on pan fish, trout, carp and steelhead. Next week I'll see if it works on salmon.
I use a regular clinch knot to attach the tippet for a droppers. I place it just above the knot that holds the fly above.