That's OK...I guess. I'd much prefer a solution that is cord only, using a break-away knot. A search of the internet didn't yield exactly what I was searching for, so I tried my own design.
Here's how I did it.
Step 1: Start with about 60 inches of cord.
Step 2: Make a bight 24 inches from one end.
Also, the diameter, and the stiffness, of the cord you choose to use will affect cord length. Be prepared to be flexible and innovative!
Step 3: Tie a decorative knot.
I chose to tie a Diamond Knot (Boatswain's Whistle Knot). Stormdrane recommends this page to help learn the Diamond Knot.
Any decorative knot will work. The Celtic Button Knot is another favorite of mine. Tie it along a single strand of cord and feed the bight back through, following the original strand back out, to form a loop.
However, the Diamond Knot is much simpler, and makes a smaller, more compact knot than the doubled Celtic Button Knot.
These dimensions were designed to fit a split ring with a diameter of 1-3/8". If you'll be attaching the lanyard loop to a ring of a different size, adjust the loop length as needed.
Step 4: Finish each end.
Step 5: Tie the Break-Away Knot.
First, tie a simple Overhand Knot at the end of the longer leg. Dress the knot tightly at the very end of the cord. This will help to prevent the end of the knot from slipping under tension.
I used a Common Whipping Knot as my Break-away Knot. Using the longer leg of the lanyard, I tied a whipping knot on the shorter leg. The longer the whipping, the more friction will hold the shorter cord, and the harder it will to break away if snagged. You'll need to experiment with different lengths of whipping and different degrees of tightness with which you cinch the knot.
Second, make a bight in the longer leg, at the same length as the shorter leg.
Third, lay the bight over the shorter leg.
Fourth, wrap the longer leg around the bight and the shorter cord, wrapping it around three cords all together. Wrap towards the bight, until you reach the end knot, and insert the knotted end of the long leg into the bight.
Fifth, pull on the longer cord to slowly tighten the knot. The tighter you pull the knot, the more load will be required to "break-away". You may have to repeatedly tie the knot and experiment with pulling the lanyard off your neck.
The goal is to have a lanyard that fits comfortably around your neck and holds your badge or whistle securely, yet if the lanyard snags on something, or a perpetrator attempts to choke you with it, the knot will break away.
Tighten the knot and then try to pull the shorter cord through the knot. If it seems to pull too easily, tighten the knot more.
When you have the knot tightened sufficiently, pull the shorter cord until its end is right at the edge of the knot.