Barking at passersby
When your dog barks at people/dogs/cars that are passing your house, they are learning that if they bark, these things go away (they don’t understand that they were never coming to your house in the first place!). The more they practise barking at passersby, the more the habit will form. In this situation, the best thing that you can do is block their view using blinds, frosted glass stickers, or moving an item of furniture they are standing on to see out of the window. Putting a postbox on your gate (rather than the post person coming up to your door) is also a great option. If they do start barking, recall them to you and reward them for the recall.