As much as it can feel like it to us, dogs really don't bark for no reason. This doesn't mean it's appropriate, nor does it mean it's something we should just ignore. But it's something we need to consider when tackling this issue, because we really don't want to JUST stop the barking, but more on that further down. There is always something driving the behavior. The dog is getting something out of it, even if all that is is a bit of a dopamine boost (it feels good).
Dogs will bark to demand something they want, convey excitement, fear, anxiety, arousal, pain, or a number of other reasons. Most commonly I see deaf dogs learning to bark obsessively out of boredom. High energy breeds (like Australian Shepherds) have a lot of physical and mental needs to be met. When they aren't, they will often resort to other reinforcing behaviors like obsessive spinning, digging, or barking. These behaviors can quickly become a default, "this sort of feels good" go-to behavior for the dog. There can also be a huge link to barking and arousal level.
Note that if excessive barking is a new behavior - VETERINARIAN FIRST.
So what can we do?
Increase enrichment
Working your dog's brain is as (if not more) important than physical exercise. Having your dog chase a ball or flirt pole is great to tire them out, but will increase adrenaline and not do much to help them learn to settle. When dealing with barking, we really need to consider the dog's arousal level, because high arousal activities will not help to decrease barking. I always recommend increasing food enrichment for your dog (there is no need for them to get anything out of a bowl). This will not only reward an alternative to barking, but will help combat boredom and the need to bark. Foraging and licking behaviors are extremely calming for dogs and help to increase serotonin in the brain. For enrichment ideas, check out: Canine Enrichment Ideas and Canine Enrichment.
Teach "Quiet"
Reward Alternative Behaviors
No matter why your dog is barking, we can take opportunities to reward the dog for doing anything besides barking. We can build a reinforcement history for doing other behaviors. This is really important when dealing with demand barking or other needs-based barking (like trying to communicate that they need to go outside). Reward your dog for exhibiting calm behaviors (even if it interrupts the behavior at first, even if that calm behavior is just standing there with a closed mouth). Here is a great video on capturing calmness.
Thoughts on shock/vibration collars, ultrasonic devices, spray bottles and other "startle" techniques:
There are several reasons why I do not agree with the use of these techniques to combat barking. The first being that one of the ways dogs learn is through associations (classical conditioning). Think of how excited your dog gets when you put on their harness or grab their leash - these are associations they've built through their learning history. Unfortunately we don't get to pick where dogs are building these associations, and startling a barking dog can easily forge negative associations with other things in the environment, including ourselves. For example, a dog barking at strangers who is startled will begin to associate strangers with how they feel when they are startled - causing an increase in stress hormones in the brain whenever they see that trigger. It can be nearly impossible to predict what our dogs are making associations with in the environment, doubly so with dogs missing their hearing or sight. It can also generally make them more pessimistic because they are afraid to make choices for fear of "failing" and being shocked/stimmed/sprayed/etc. This is especially important for our impaired dogs because we are often unsure of what exact triggers are because they aren't always obvious.
Another reason I don't recommend these tactics is because startling the dog only suppresses the behavior. Suppressing behavior does not mean that a productive one will take it's place. Punishment in this case increases stress hormones in the dog's brain, and we see this pop up in other areas. I equate punishment based techniques like this to holding a beach ball under water, because we very frequently see things like anxiety pop up in other areas because it has done nothing to change why the dog is barking. It has done nothing to help the dog's emotional state. This is simply bad training and unfair to our dogs, especially those that cannot see or hear.
Now what?
If none of this seems feasible for you and your dog, please find a Certified Professional Dog Trainer near you. A trainer can help you identify your dog's triggers and come up with an appropriate training plan specific to your dog.
Keep in mind that the dog training industry is completely unregulated, so find a trainer that keeps up with the latest research and is always continuing their own education. I recommend starting here.