After running into this a while ago when I was rebuilding my system and getting annoyed by all the different things that try to modify it, I ended up giving up and just setting the file to immutable. It has been working fine for the past couple of months as nothing seems to autodetect the flag and try to remove it.
I started doing this exact same thing in Debian, I think around Wheezy. Lately I’m back onSlackware and a little *BSD. Thankfully these systems still go the traditional route so it’s not much of an issue anymore.
I have used this in the past. There are only a few places where this bites you, for instance wifi authentication portals. Some of these wifi access points change your resolv.conf so that you can load their internal page for terms and conditions.