This is a "hack" we learned from a friend of ours that is a veteran of Israeli special operations forces. Not every country has the budget that the US military has and when one thinks about the sum total of the bureaucracy required to design, develop, stock, and manage the supply of specialized one-pass or NATO-style straps this trick is a model of Israeli ingenuity and resourcefulness. The simplicity of the solution is several fold 1) it's inexpensive 2) it doesn't require specialized tools 3) it takes advantage of mil-spec cordage that is widely available and 4) it'll keep the watch secure but at the same time break away/slide off at the point when you'll start wondering whether keeping your hand or the watch is your top priority.
Tools: "95" Paracord, matches/lighter, sharp scissors
Tie a double not around one length of the paracord. At this point it doesn't matter where. The important thing is that the one end of the cord can slide back and forth through the knot. Make the knot as tight as you can. (If you are more skilled feel free to substitute a more attractive knot.)
Cut off excess paracord from the knotted end.
Fitting the Watch Keeper to the Watch
If you have the standard fat or "skinny" fat bars fitted to the watch you can use a toothpick to unseat the spring bar. This will prevent damage to the exterior of the case.
Lay the loop on the watch as shown.
Fit the strap or spring bars to the watch making sure the loop is between the spring bar and the case body.
When wearing the watch first fit your hand through the loop and then fasten the watch strap. After the strap is secure move the knots away from each other so that the slack is out of the way.