How small is too small a caliber for self protection?

Subject: How small is too small a caliber for self protection

"Woman stops gator attack with a small Beretta pistol."

This is a story of self-control and marksmanship by a brave, cool-headed woman with a small pistol against a fierce predator. What is the smallest caliber that you would trust to protect yourself?   A Beretta Jetfire testimonial:   Here is her story:

While out walking along the edge of a bayou just below Houma, Louisiana with my soon to be ex-husband discussing...