I was just reading about pepper spray repelling a mountain lion...what about using one of those very loud boating/marine fog horns? These horns are quite small but can be very loud.
Yeah, sure. Why not? Eventually the mountain lions in your area will equate a loud "HONNKKKK!!!!" with…food. So go for it.
The Gear Guy
Seriously, maybe it'll work. There is some evidence that noise drives off cougars. But mountain lions aren't bears. As a rule, a bear would rather clear out than confront you—even letting a mama bear know you are near is better than surprising her visually. But mountain lions (aka: puma, cougar, catamount, panther, and so on) are different creatures. They stalk. So any sound you make may ATTRACT them, not deter them.
That's also the trouble with pepper spray. In most accounts of bear attacks, the hapless hiker stumbles across a bear, and the bear then charges. You aren't apt to even SEE a mountain lion. They will creep along in the underbrush, belly on the ground and quiet as damp tissue, and then pounce.
So, the best strategy is to avoid them all together. Try to avoid hiking with pets in cougar country, and be cautious at dawn and dusk; cougars are crepuscular creatures, and most active then. Go ahead, look up crepuscular. I’ll wait.
OK, done. Also there is some evidence noise will drive them off.
Still, you might see a cougar before it attacks. Mainly, it's a matter of knowing what to do if you see a cougar. Make yourself big—raise your arms, stand tall, act nine feet tall. Give the animal room to escape. And if you have something handy to throw at the cougar—your hiking partner, for instance—do so. But don't bend over to pick up a rock. Stay big. Pepper spray? Maybe. I doubt you could hit a cougar once it charges. Better to punch it in the nose. But once it is that close, good luck.