Three years ago, my wife was out walking our poodle in the snow, when a great Pyrenees got loose from his master (a judge), ran up, knocked my wife down and bit her on the leg. She was protecting our dog. The owner of the attacking dog threw himself on it and got the dog off her. The bite was close to a major artery. If it had torn the artery, my wife might have bled to death. Something like half a million dog bites are reported each year, and many involve children. Something like close to 5000 mailmen are bitten by dogs each year.
When I walked our dog, I carried a Rookie in my pocket, but also carried pepper spray and a 3 ft. stick. I originally got a garotte from Kris Cutlery, but found it wasn't strong when testing it on a cardboard box. I carved one for myself out of Argentine lignum vitae. A long walking stick of 3-4 ft is the best defense, according to a local police officer. Even an umbrella can work - it did for my wife in a later incident.
At night, I carried a 4D maglight, with a very bright Malkoff Devices LED insert. One night a strange dog ran up to us, I turned around, the light flashed in the dogs eyes...and the dog jumped in the air and ran away.
I'd recommend the Caly3 that you described. I have one, and it is a very quick opening knife. The action is smoother than my Rookie. It is highly recommended.
Personally, I'd want the long stick and pepper spray. You don't want to be close enough to have to use a knife to defend yourself. It is windy here in Illinois, so my first line of defense would be the stick! If nothing else works, then you can always use the knife.
There have been a number of dog attacks where I live, and they often are directed toward someone walking a dog.
P.S. the offending dog got house arrest for a few days, and the judge's homeowners insurance had to pay for my wife's jeans. In Illinois, dangerous dogs are allowed "3 free bites" before being declared dangerous.
Wow, that must have been a terrifying experience. I'm glad your wife is okay. That pyrennes should have gotten the needle, IMO. Dog bite laws are often too permissive. Our love of animals is clouding our perspective.