This weekend I had two dog encounters in one day during a solo weekend trip, and thus I spent a lot of time thinking about what the best way to deal with dogs is.
The question: What do you do when a dog is much closer to you than its owner (off leash), and it is possibly acting aggressively towards you? Assume it's just you, no friends around you.
1. Hiking through a willow meadow that is long and narrow at around 9AM, I was minding my own business walking along, trying to apply sunscreen without stopping. I heard a noise behind me, like grass brushing, and I turned around. There was a huge dog 5 feet behind me, with no owners to be found. Seriously, some bears are smaller than this dog. I was startled, and that made the dog bark and growl, and hold it's ground. I pulled out my trekking poles with one hand, put out the "stop" gesture with the other hand, and firmly said "No." Luckily, the owners were camped a little ways away and called their dog off. I am not sure my tactic would have worked.
2. Same day at around 3:30, nearing the trailhead. A family is day hiking up the trail with several dogs. Two of the dogs come running, and don't seem aggressive. One of the two, a black lab, starts growling and barking and doesn't come any closer. The dog's owner calls the dog back, and I proceed to go past the group. While I am going past, the dog once again growls, and gets close enough that I have to put my poles between me and the dog, and push the dog away.
It seems that I should worry more about people's dogs than bears and mountain lions.