Reference: Gelert, protection (dog)

Another great historical/mythical dog guardian is Gelert. Again, with this story, there is a proverb: "To repent as deeply as the man who killed his dog." The Welsh phrase comes from a 13th century folktale which tells of Prince Llewelyn's favorite wolfhound, Gelert. One day the prince was hunting and he noticed that Gelert was not at his side. Returning home, the prince was greeted at the door by his wolfhound who had a blood-red mouth. Inside, the prince saw his son's cradle overturned, and the house in total disarray.

Thinking his dog had killed his son, Llewelyn drew his sword and slew Gelert. Then he heard an infant cry from under the cradle. At the same time, he caught sight of a dead wolf in the corner of the hall.

Grief-stricken, Llewelyn built a stately tomb for his brave dog. And so it was that the village Beddgelert, which means Gelert's Grave, received both a name and a saying; one that has survived through the ages.

- Gerald Hausman, "Dogs, Ancient and Modern: A Mythological History"