...Dogs of all ages who are fearful, anxious or aggressive.
I don't like it, you don't like it, and dogs don't like to be fearful of anything. Dogs have the same "feelings" we do when we choose to avoid a person, place, or thing due to the belief the thing may hurt us.
Now they must decide how to cope with the situation. They may choose to run, they may stand their ground, they may put up with the thing but feel terrible while it's near them. They may wait for you to pick them up and remove them from the situation.
They might think biting the thing (person, animal or object) is the only way to make it go away.
The best solution is to teach our dog children that the thing they thought was scary, is in fact, a lot of fun. Yes, it's actually possible.
What is your dog afraid of?
Is the thing a real threat? If possible, remove it from the dog's life. If the threat is another pet, let's get that pet in training and repair the relationship.
If it's a phobia, that is, the dog "thinks" its a threat but it's actually not, let's communicate with your dog. Everything is fine, the vacuum is not going to eat you, and we can prove it by using individualized reward-based training, which is called positive reinforcement.
By the way, the word reinforcement means we give your dog something they like when they do what we want. This makes the new good behavior more likely to happen again and again.