You can see the rear half of the one I made out of an aluminium sheet and an L-bar in the video below. After a few years on the bike, I took it off because it was hard to maintain.
https://www.youtube.com/watch?v=Pl4088Dbs4A
is that on the inside of the chain also?
I think I’m gonna use one of those fold-y front mtb guards, a mudguard stay shd pinch it for the lowest ring and hopefully it’ll flare out above that to keep the tyre crap off