I have only walked one truly dangerous dog, and eventually his owners had him euthanized because his behavior was so unpredictable. He would be fine with some people, and other times he would lunge at someone for no reason. He would walk past dogs a dozen times and ignore them, the next time he would be enraged at the sight of the same dog a block away. Walking him was not fun, mostly because he gave almost no cues. His posture/attitude wouldn't change until a split second before he acted - it was total defensive dogwalking, avoiding anything and everything that might set him off.
I watch my dogs all the time while I am walking them. I don't listen to music, and if I need to use my cellphone, I stop walking, make or take the call and then continue. Part of this is liability control - they are not my dogs and I am responsible for them when they are with me. Every day I see dog owners - and dog walkers - walking, oblivious to both the world around them and the dogs' behavior. They don't realize there is going to be a problem until it is happening, and by then it's too late to do much about it. They are constantly surprised by their dog's behavior because they don't see all the cues that occur beforehand. Any correction they make at that point is ineffective because it's too late.
Let's take a typical scenario: Mr. A is walking his dog, Brutus. Sometimes, Brutus lunges and barks at other dogs, surprising the hell out of Mr. A, who considers dogwalking time an opportunity for quiet contemplation of...whatever. Dogwalker, Ms. C, avoids Mr. A whenever possible because she knows he is completely oblivious to what his dog is doing. Brutus gives perfectly clear signals that he is going to lunge, by the way, obvious from the moment he spots another dog. He is okay with female dogs, but dislikes large male dogs a lot. Mr. A has stopped trying to correct the behavior because he doesn't see any improvement when he does make a correction.
Dog training, like comedy, relies heavily on timing.
When Brutus sees another dog, he assesses the dog's threat potential by scent, visual recognition and the attitude of the other dog. Depending on what he sees, he then either continues on his way or slows his pace and stiffens his whole body. (Some dogs will go into stalk mode, lowering their head and creeping toward the other dog.) Right then, when he slows and stiffens his posture, is when you need to redirect his attention. This is where you need to know your dog, and tailor your action to their personality. You can say their name, bump them with your leg, tug the leash or step into their path - or some combo of those - but the important thing is that the dog must look at you and not the other dog (or skateboard or whatever). When they look at you, then you can tell them either "no - leave it" or "I don't think so" or simply, "walk on". The important thing is to make clear what you want them to do - walk quietly and ignore the other dog. The more important thing is that you need to do this first time, every time, no excuses.
Lunging and barking at other dogs is the reward for the stalking behavior - which is the real "bad" behavior. Once the dog is barking and spraying spit at the other dog, he has already gotten what he wanted, and any correction or punishment at that point will be ineffective. You need to address the stalking/stiff posture/defensive pose by redirecting their attention to you, and encouraging and rewarding appropriate behavior.
Oh, here's an example of bad timing, by the way. I would see this guy walking a Benji-type dog all the time. At first, the dog was friendly, but very often the guy would pull the dog away and avoid other dogs for no apparent reason. Over time, Benji got suspicious of other dogs and began to bark as soon as he saw them. In an attempt to stop the behavior, as soon as Benji would get excited and bark the guy would give Benji a treat and ask him to sit. Are you with me so far? What happened was that Benji's barking frenzies got worse and worse - because the owner was rewarding the barking.
And my personal favorite is when I hear someone tell their dog, "Be nice!" in a conciliatory tone, as in "Oh, Brutus, be nice to the other doggy," while Brutus is doing his very best to get a piece of the other dog. This just makes me want to smack the person saying that. The dog does not understand what you are saying, and you've just made it clear to me that you are absofuckinglutely clueless and the dog's behavior is all your fault. Bad human!
This isn't a one-time deal. Behavior modification takes time, patience and attention to detail. So the next time you walk your dog, don't try to multitask, and pay attention to your dog's body language.
