Oh wow, and I thought Gunther's nails were bizarre. I have no suggestions but I feel for him. Gunther's nails split easily too but nothing like that. I normally just have to peel off a small edge piece. that really does look painful.
Gunther last month ripped off part of his nail. Really he ripped off part of his quick, with the nail still intact. the outer nails on all his feet (so 8 nails altogether) have growths (almost like a callous) that grow beyond the underneath of the nail (unlike most dogs, whose quick is flush with the nail). He ripped off the portion protruding beneath one of his nails when we got a layer of ice on top of snow several weeks ago.
Only now does it look like it's finally healing up. For awhile there ever time he went outside it would start bleeding again but I really didn't want to wrap his foot b/c the area needed to harden up again.
Not only that, but every winter he scraps his back legs to bleeding on his hocks. He is so accident prone with his feet.