Okay, don't know if this has been tried or posted before but I have tested this new method for a couple of hundred miles and no problems or lost magnets.
You know what powers those electric toothbrush heads???? Magnets, two small magnets. When changing heads, I have saved mine for my tool box for a couple of years and they come in very handy.
Well, I thought I would try them on the inside of the crank arm on the back of the pedal stud. Adjusted the cadence unit so that everything aligned and they work great! I think I fit three of them in there but I'm sure two would work as well. Since they are recessed into the crank arm, they won't (or haven't) fallen out and have plenty of power to trigger the sensor.
I was always cutting the magnet strap when I clipped in. Went through three magnets in a couple of months. Well, this solution works for me...hope it helps some of you.