The 9mm should do the trick if hit in the vitals. The problem with cougars are their stalking nature. You are not likely to see one till too late if they are indeed a threat to you (which should be fairly rare under most situations). Otherwise a rifle is a better choice as they will typically be too far away for a short radius sighted weapon (unless scoped).
A big tom was spotted on our lease. I carry a 357 just in case, but I realize my odds of using that weapon are small.
A friend sent me this picture. I don't know the story behind it, but it's one big [color=#FF0000]█[/color][color=#FF0000]█[/color][color=#FF0000]█[/color][color=#FF0000]█[/color][color=#FF0000]█[/color] cat.