Going back a few posts the idea of waterproof socks was raised.
A short while ago I invested a pair of Dexshell waterproof socks: https://dexshell.co.uk/
They got their first test today on a decidedly autumnal run over Ingleborough. The ground is very wet at the moment, with loads of puddles to splash through. I could feel the water sloshing around in my fell shoes (as usual) but my tootsies stayed warm and dry (which is far from usual!).
I didn't go in over the tops of the socks and I don't know yet how durable these are, so this isn't a "review" as such. But heck, they were certainly comfortable!
The above is slightly off topic but may be of interest to some. Back on topic, it was suggested above that tucking trousers into socks might cure the sock sag problem. I often walk up to potholes in a pair of Ron Hill Tracksters, which are so thin I doubt it'd work. But the suggestion gave me the idea of trying the foot tape over socks, which I've never bothered with before. (This is the nylon "strap" that goes under your foot to stop the Tracksters riding up.) I wonder if that'd help?