I had a few slip on me too until I worked out how many turns work with what lb leaders. For me, the trick seems to be to put a little tension on the braid loop and the leaders tag going thru it, whilst pulling up the rest of the knot. Experiment, but doing this helps the leader to start to spin around all your braid turns much earlier and this seems to make the knot more reliable than when it all just spirals into place at the end. This knots also called the bristol yeah? If it is, I've seen it recommended with as few as 7 braid turns/wraps in a few places.