Pheremones. Available from many vets and on-line is the DAP (dog appeasing pheromone) diffuser, a plug-in device (very much like some air fresheners) which mimics the properties of the natural pheremones of the lactating female which gives puppies a sense of well-being and reassurance.
This product is available as a spray for the car and now also as a collar so the dog is under its influence at all times. The plug in diffuser continuously releases the active ingredient into the dog’s environment. It is detected by the dog’s sense of smell, giving out comfort signals to help alleviate fear and stress. DAP is odourless to humans.
Visible improvement in specific behaviours may take some time depending on the severity of the problem.