The final behavior has the dog responding to the cue (of another person approaching the defined perimeter) by moving forward and across the handler so the dog's body forms a barrier between the handler and the approaching person.
We have, as a preliminary behavior, the ability to move the dog into any desired position around the handler's body with the use of the hand target (dog's nose to target). The behavior we need must be further defined as the dog's response to the approach of the other person. To that end, we start by focussing the dog on the approach by asking for a touch of the other person's opposite hand.
Stitch 1: Touch
Stitch 2: Touch/Touch
Stitch 3: Touch/Touch Food
Stitch 4: Touch/Touch Food
Stitch 5: Touch/Touch Food
Lily 1: Touch
Lily 2: Approach/Touch
Watching for the dog to acknowledge the approach of the stranger and then offering the target hand as the dog positions herself between stranger and handler.
Lily 3: Touch/Touch then Approach
Lily 4: Experiment
Permitting an approaching person to speak to and interact with the dog is contra-intuitive to the purpose of the desired behavior.
Lily 5: Confusion and Recovery
Here we can see the confusion of the dog as to it's correct response. We recover by reviewing and reteaching the proper reaction of the dog.
Lily 6: Dropping the First Target (still recovering from experiment)
Lily 7: Refining (still recovering from experiment)
Next: Approaching person arriving around the clock (front, either side, back).