Thanks. Good photos.
I have some of those, they can be bought at an office supply store.

I just use wire, I bend it around the outside of the fender, bend a small section around the inside on each side and just crimp it with pliers. One benefit of both methods is that if the flap gets caught on something, it can pull off without damaging anything else. I like flaps that almost touch the ground when stopped. Of course then it needs to be very flexible. I use MBT inner tubes folded back on them selves and glued together. One layer will just go back to the original shape of the tube. This makes a flap so soft it moves out of the way for snow even. Or water, rolling over logs etc. Like I see in your ride photos. I enjoy your ride photos.