Found this knot on Capt. Mark Block's website. Haven't used it in the field but have tied it at home. Seems to hold very well.

Everyone always asks about the loop knot I use - Which, by the way, I use about ninety percent of the time, regardless if I'm fly or spin fishing. I learned this knot as a "MirroLure" knot, but haven't heard anyone else call it that. It is a simple knot that can be used in just about any sized line or leader from six to one hundred pound test. It can be tied very quickly, even in the dark, but more importantly it makes for a quick lure or fly switch when necessary.

Tie an overhand knot loosely in the line

Note: The yellow lines indicate which strand of leader is overlapping on top when two strands cross - The yellow is the top strand.

Run the tag end through the eye of the hook, and feed it back into the overhand knot

When you go back through the overhand knot be sure to go back in on the same side that the tag came out

Snug down the overhand knot and slide the tag up or down to adjust the size of the loop you want

Tie a half-hitch around the standing line with the tag end

Tighten by pulling both the standing and tag end of the line

ALWAYS sharpen the hook

Also, if you flatten the barb it will make for an easy release

Tried to post the pictures but they would not go. Here is a link to his site; http://www.everglades-fishing.com/fishing-knots.htm