Problem Solved! Eliminating heart-rate monitor chafing once and for all.
There's just one downside to wearing a heart-rate monitor: the painful chafing that causes awful irritation while I'm running, and leaves scars behind. After trying lubricants (putting BodyGlide under where the strap & sensor are), or putting soft electrical tape or a band-aid around the edges of the heart-rate strap (thanks to DC Rainmaker for that suggestion), or rotating the sensor around and wearing it on my side, or on a different place on my chest, and STILL getting chafed, I finally stumbled upon a solution that works for me: leaving my heart-rate strap "as is," and instead, covering my skin with medical tape.
There are lots of different kinds of chafing; I experience it in the center of my chest (and always in the same spot, regardless of where the sensor sits):
To do away with chafing like this, grab a roll of white standard porous medical tape (cheap, available at any drugstore):
Apply the medical tape over any areas where you're being chafed. I typically use two short strips, and that does the trick. It may wrinkle a bit but that doesn't seem to make a difference:
Then, wear your heart-rate monitor as usual, and enjoy some happy chafe-free running!
See you on the trail!