I am not a guitarist (I never got very far with it, partly because of the sore fingers) but my brother, who played a lot at one time, used to apply nail hardener, not just to the nails but to the fingertips.
Official disclaimer: this is at your own risk. If you try it and you develop gangrene, or your fingers stick to the strings and leave you looking a fool, I cannot be held responsible, OK?

Marje