CASTLE ROCK, Colo. (KDVR) — There’s an old saying: It’s not the size of the dog in the fight, it’s the size of the fight in the dog.

Castle Rock’s own Luna “the tuna,” as her humans call her, proves it to be true.

“She’ll boss you around,” said Luna’s owner, Jordan Courtney.

“She loves to tell you when she wants anything,” Courtney said. “Luna is a little spitfire.”

Luna stands all of 6 inches high, but don’t tell her that.

“Why would she in her right mind chase a full-grown bear?” Courtney said.

Why indeed, but Luna met the moment despite her true nature.

“She’s just a chill, at-home dog but she loves to chase anything down when she sees it in the front yard and the back yard,” Courtney said.

She’s a regular enforcer on her block in Castle Rock. She’s the first line of defense for the Courtney family, morning, noon and night.

“She is protective of her family. She just wanted to protect the home front,” Courtney said.

Tiny pup confronts an extra large threat

Courtney said it was about 2:30 a.m. when her mom took Luna outside. Luna knew before anyone that there was an unwelcome visitor near their home.

“Then Luna went racing off, barking, and my mom didn’t know what she was barking at,” Courtney said.

Video was caught on their neighbor’s security cameras — not that Luna needed a reminder of how much of a good girl she is.

“It was just comical, seeing this little doggy chasing after a full-sized bear,” Courtney said.

Colorado Parks and Wildlife reminds folks to report any bear sightings in their neighborhood so officers can track the animals and monitor them in case they return.

Unlike Luna, CPW advises not to chase down any bears.