Far too many people observe a dog reacting at something and they automatically assume that the dog is fear/aggression. The best way to determine if your dog is experiencing frustration is via history of the dogs behaviour when off leash with other dogs. Do they typically play well with others? Aren’t sure because you haven’t tested the waters? If you are really worried about the safety of others and your own dog you can take the time to desensitize him to a muzzle, just don’t rush that process otherwise it may cause even more frustration.
Obviously a sudden appearance of something that startles the dog is causing the dog fear. However, what about a well socialized dog that reacts at other dogs when on leash, yet the dog has no bite history, years of off leash play without incidents, regular dog friends and dozens of leash greetings that go very well, yet the dog barks at other dogs when on leash when they cannot greet and even when they can greet, the dog barks. That dog would be considered frustrated not fearful, yet many people would label the dog fearful.
This misinterpretation of the dog’s reactivity could eventually hamper the dogs socializing but don’t be persuaded to peruse harsh methods to stop the barking. Humans that allow some leeway to the dog’s barking do much better in terms of results and eventually reducing the dog’s stress to acceptable levels. Fear is not an easy thing to spot for many people. Dog walks are intrinsically distracting for humans and canines. Many dogs “tough it out”, then one day start exploding, as the whole time they were not barking, or maybe barked but were “shushed”, they were still fearful. Bottom line; if you aren’t sure contact a qualified professional using science-based force-free methods to ensure your dog is never harmed in the process of training.
What we can do: DRI (differential reinforcement of an incompatible behaviour, in plain English let’s teach the
dog a skill that is not compatible with barking to PREVENT reactions while on leash. It could be disengaging… looking at the dog and then looking away, it could be giving you some eye contact, hand-targeting…. whatever is easiest for your dog. A well thought out training plan will include working from a distance FIRST because expecting your dog to respond to your cues if they are too close is not realistic.