and don't forget that in some areas and at certain times of the year -- there is the possibility of snakes (both poisonous and non)
As far as bears -- it has been suggested that you wear bells to scare and ward them off. While walking in bear country keep a look out for signs of bears -- bear poop is a good indication. Now for the tough part, telling Grizzly Bear from Brown Bear poop. Just remember that Grizzly Bear poop will have bells in it.
Actually the best defense is geocache with a friend that you are able to outrun.