I have had the same problem with a couple different large dogs. Only thing that worked for me was the open diamond shaped metal mesh - not sure what it is called, but it is about 1/4" thick, not bendable like fencing. It stops them when screwed flush to a door. It is not a pretty looking fix but it worked. If it was not flush, they were able to get their nails behind it and pull it loose (screws gave way). Good luck.
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