Yesterday's shooting at Fort Hood was the most violent in history on a US military base, with 13 people confirmed dead and dozens more injured. With stress disorders taking an increasing toll in the military and thousands of combat veterans struggling with Post Traumatic Stress Syndrome, mental health has become one of the most important issues facing soldiers today. For some, help may be coming from a surprising place, dogs that are trained to deal with PTSD and other problems. They're also playing a critical role on the battlefront. So how much can man's best friend do? What are the limits of canine therapy?