Since almost every hike or other backcountry excursion I do involves carrying bear spray, I always have some "expired" stuff around. A few years back we had a serious problem dog down the street, who chased kids, cyclists (including me), old ladies on walkers, everyone. The dog and his dog pal snarled and growled and nipped and his owner said the dogs needed their "freedom" and he was not going to tie them up. I decided it was a good a time as any to test my old spray canister. So one day I headed out on my bike, and sure enough they came out ready for a chase, so I gave them a good dose. It was quite effective. Only one of the two really got a face full, the other just a bit, but they both backed off immediately. Neither has chased me since, whether I'm on bike or on foot. They've stopped chasing others as well, and just bark from their driveway. I learned a lot from that test, such as maintaining awareness of wind direction (I got just enough drift to have to cough for a few minutes), that the spray is under pressure sufficient to throw off your aim unless you're steady, that the pressure produces a startling bit of noise, that the spray is brightly colored and stains, and that you have to aim low, as though putting out a fire with an extinguisher, in order to come close to the face of a shorter animal. I've tested several since, including during a class at Denali Park with a bear expert, who gave us additional tips for its use, such as always keeping it ziploc bagged when not in holster, due to potential leakage. There's nothing like building confidence with firearms or pepper spray, preferably long before you need it. I would echo David in that it's inexpensive enough to be worth practicing with it if you plan to count on it in the field.
