Yep, exactly as you say, older bitch my lad's got, plenty of roadwalking, easily 40 + miles per week, walked twice a day, apart from days/nights she gets worked, along with free running etc in fields and working, never seems to make any difference to her nails, especially on front paws, constantly taking very small amounts off them, roughly every 2 weeks, they grow very quickly and you can't do too much in one go as she also hates having it done.
Dunno if it's the deerhound in her, but she's got some of the strongest nails I've seen, strong but a pain to keep on top of
Does it affect he