Systematic Desensitization & Counterconditioning
If the cause of a dog howling is his feelings about something, then teaching a behavior such as fetching a ball would not be a good solution.
You should try to change the feelings or motivations that are at the root of the problem.
Fear, anxiety, phobias and aggression are treated with systemic desensitization. It can be used for any behavior problem that involves emotion or arousal.
Combining the two methods will yield better results when trying to correct a behavior problem in your dog.
Hire a professional who can give you advice on how to use these techniques individually or together.
