Hi quizmad- I have looked through dog breeds containing 9 letters and none of them seem appropriate to the clue so think it must be a fictional character. Sounds like a real old toughie to me. Good luck.
If you Google "fictional dog names" you will get over 270,000 hits - dogs in film, television,cartoons etc. Also been through list of 9 letter dog breeds in Crossword Solver - nothing fits