I am reading an article in October's Runner's World right now about the Garritson family. First of all, I had never heard of them. Apparently, they are a family of 16 (!!) that are all involved in running. They've been in the news off and on since the 1980s because of their "extreme" lifestyle.
The article is about how when out for a run in the hills of California in November of last year they were attacked by a pack of 6 dogs.
Here's a news story about it. I'm not done reading the article in Runner's World yet, but WOW it really gives you a lot to think about as far as safety while running.
I have only ever run into one loose dog while running, a yorkie, but there are plenty who bark at me through fences when I run past. I've been considering buying a pepper spray keychain to take with me while running, and this article has given me the push I needed to go ahead and order it.