hii,the problem you are facing is due to unfavourable socialization of your pet. this simply means that your spitz had an unpleasant encounter with aggressive stray dogs during his younger days and that's why a sense of fear is instilled in him.it'z difficult to socialize at this age but still you can try the technique of avoiding forceful interaction with new member. for further details kindly check https:// or mail me directly at gmail.