i spend a month a year in bear country,two weeks in the spring,two in the fall.this is in the wilderness canoe area in northern minnesota.i have two sprayers,both are police style because the ones marked for bear use are too expensive and IMO not any better.one is a large foggier and it's carried in a day bag and them set out near the cooking area in camp and then in the tent at night.the small belt size one also is carried in the day bag inside the canoe but on "iffy" portages i put it my pocket."iffy" is hard to nail down but you get an idea of places where you might run into a bear after a while.
the only bears i have ever seen in 25 years were all running away.
i stay away from busy areas where there are well used campsites and try and get off in more remote places,i call them hidden camps,the fire places sometimes have seedlings growing in them.
now about how to use one.i assume that the black bears i might run into are going to be camp bears,some places you have no choice but to camp in a used area.so the bear is not going to come charging out at you,even on the portage i don't think a ambush is at all likely.so you will have a chance to prepare your shot.
first put you arm across your nose and mouth,pull down you hat if you have one to cover more of you face and just before you shoot,if thats the right word,close one eye so if you get blow back one eye will still work.don't aim for the bears head,its too small rather fog the ground in front of it.
bears are like getting hit by lighting,it could,it can and it does, but so seldom where i canoe and camp it's not something i worry about but am ready for.i know it's another story out West.