Thanks for the report on the DT axle - that was going to be my next attempt if my custom fix below didn't work. I'm glad to hear the DT axle is performing well.
I fixed my loosening rear axle by doing this:
1 - Blue loctite on the threads
2 - Two rounds of Gorilla tape around the nut. As in, around the smooth circular part, not the wrench flats. I did this to fill up the space in the bracket, allowing that little set screw to dig into it.
3 - Carbon assembly paste on the contact surfaces at both ends. Probably not doing anything, but I was going for overkill.
4 - Quick release lever oriented upwards, so it can't unscrew (it would hit the frame if it did). It's not actually contacting the frame, but if it did start to rotate counterclockwise, it would make contact and stop.
I drew a small orientation mark on the nut and bolt (silver line the first photo) and can see that this has not budged.The tape is neatly trimmed so you cannot see it. I am no longer angry at this axle!