I just got back from the Fox site and the products they show seem to be VERY low powered compared to what I've had. First of all, I used to carry a small mayonaise jar, about 3 oz. I guess, filled with pure FRESH Capsicum Cayenne pepper powder made into a soup with grain alcohol. This is what was used in Alaska for Griz.
Temperature does affect pepper spray, in the cold it does far less damage. I prefer 20% or stronger sprays as I am NOT going to use the stuff in less I must. By the way, the spray even when not used goes bad in a year of so, so you must get fresh cans once a year or so.
Fox has only 1% to 5% sprays according to what I saw. Here is some 10-15-20% Oleoresin Capsicum
http://www.peppersprayinc.com/otherpeppersprays.htm
Some good data:
http://www.aware.org/rhot.htm
What I've used is a walking stick made of Hickory or something NOT biteable or breakable and fixed with a point. Mine has a long metal point. And using it to give distance by pointing it at the mouth of the dog. If the dog seems is in range then perhaps a quick Pool-Shot like your first shot, with a long and powerful follow through down the throat, with a quick pull back and prepare for second shot could be in order. Swinging a stick is NOT my preference as some dogs have developed defense and/or attack moves against a swung stick.
I've had to kill one wild dog by hand and it was FAR harder and took FAR longer than I would have ever believed. The dog charged me, and I charged it; coming up under the throat I grabbed it hard with my left hand under the throat as hard as I could and held on. I had a heavy, short, Corpsman's Machete on my right side and took it out. It was razor sharp, heavy and had a short, about 16 inches, 1/4 inch thick blade.
I hacked and hacked with all I had into the base of the skull and spine as the dog continued to try and get me. This was only about a 50 pound dog and I was holding it off the ground by the throat the entire time. I think I chopped it, with all my might, about 30 times into the spine.
My three year old son was with me and was the initial target of the dog. There were five other larger dogs about 15 to 20 feet away from us in a circle barking and snarling. I was really trying to finish the first dog with every single stroke including the first one as I figured I might have five more dogs at least to defend ourselves against. The first dog finally died, with lots of noise as I chopped it. I also was making LOTS of noise, in hopes that the other dogs would stay put for a while.
Once the dog went limp in my hand I chopped it a few more times in the same place on the spine, just behind the head, until I went all the way through the spine which was a lot easier once the dog stopped fighting me. AS I was chopping through the spine of the first dog, I was looking to see which dog was going to come at us next.
A second and much larger dog lunged a little closer to us than the others. I gave a war cry, as I held my son closer to me with my left hand and started toward the dog with my machete raised. All at once that dog fled and the others with it.
I don't want to EVER do that again.
My preference, now, when in the woods with possible dog problems... is along with the walking stick, my Glock 19, hi-cap with Quik-Shoks and an extra magazine.
Several other times, three or four I think, I've backed down dogs with a loud attack, straight at the leader.