The simple truth is that even if the attack by the dog succeeds
the bad guy is still going to be alive to contradict everything you say... hopefully there will be witnesses but if this is a pro-bad guy then there probably won't be.... So, then there you are with a chewed up piece of scum telling everybody "this person's dog attacked me.... I wasn't doing nuthing.."
I love my dogs and they are much better at telling me when something or someone is around...but as for protection... I'd lock them in the bedroom first.