I build leaders with nail knots and double-overhand knots. Make a double-overhand in the thicker leader material, leaving the knot in a loop to thread the thinner leader. Then a nail-knot, using two wraps after the initial loop for the thinner section. Then pull / secure both knots. I also use a two-wrap nail-knot for attaching a fly to tippet. The practice is far stronger than a clinch or blood-knot, likely because the nail-knot wraps are not as subject to tension, but rather, the tension is paired with compression from the wraps, and the double-overhand is only acting as a stop and the thick mono is being compressed.