One of the more difficult conditions to deal with in many dogs is separation anxiety. This is exhibited by the dog acting out when they are not round humans or other dogs, and are left alone for periods of time. Typical separation anxiety behaviors will include incessant barking and howling, scratching doors and windows, destroying furniture and bedding or urinating on carpets. The dog will probably only act this way when left alone, and training is necessary, combined with exercise, to break the habits.
Dogs that act out when they are left alone will generally have learned this behavior from the times when they were puppies. When they are first brought to a new home, it is probably the first time they have ever been away from their pack and naturally they are feeling stressed out by a new and unfamiliar environment. Our first reaction to attempt to help the new puppy cope with being alone for the first time in their lives is to shower them with attention, and to socialize them as much as possible. Sooner or later this same animal is going to have to be left alone, and the learned behaviors are going to come back. When the puppy cried or howled when left alone, you probably came back and showered them with attention because you feel bad that they were sad. What you have actually done is reinforce that if the puppy howls loud enough they will get attention. Even if you verbally reprimand them for acting out, they will probably view this as reinforcement that they will get attention if they act this way. In addition to this, a dog who is left unsupervised has nobody instructing them on what to do, and a lack of training in this environment allows the dog to make their own decisions, which are probably not the best ones. They will amuse themselves by destroying things or barking incessantly, which is not corrected on the spot and therefor is never taught to be wrong.
Exercise and training are the best way to deal with separation anxiety in dogs. Making sure that you walk them as often as possible, especially before you are going to leave them alone, will get rid of a lot of the pent up energy that becomes frustration when they are left alone. Making sure they are trained that the bad behaviors that they have been exhibiting when you are not around are actually not a way to get praise and attention is accomplished by not showering attention onto your dog the moment you walk into the house. Even though you want to say hello, the dog is assuming that their acting out has brought you back and causes them to get affection…it is the wrong lesson to teach. Leaving your dog alone in a crate for longer and longer periods of time after walking them will be the best way to train them to be alone. It is going to be a slow process, but eventually the dog will understand that he should remain calm while you are gone.