I adopted two previously abused female chihuahuas and been working on them in obedience. However, they're still very frightened of strangers, dogs, and new experiences. When they are inside the house and any of the above enters, it becomes a barkfest. When we encounter those things outside, they cower into me. They also bark/whine when I leave or return (after I'm gone/return for a while they stop). How would you go about socializing and training them? Currently I'm using Clicker Training. Any tips or advise would be welcomed!