Does walking with a big dog deter potential attackers?

I'll just tell you from personal experience...I walk a trail that goes through a wooded area, and though it's on a military base, I still take my yellow lab. A guy was running the trail and stopped to try to talk to me, and my dog stepped between us, let out a low growl and let him know right quick that he was to back off. I feel much safer with my dog with me. It may not completely deter a determined attacker, but I think it makes you a less likely victim.