I just got a 3 month old female retriever/pit bull mix and she won't walk. When we are in the yard, she is fine, stays somewhat near me, but when I put a leash on her, she won't walk. I tried putting a light chord(string) tied to her collar but she still sits and won't move. Today I dropped the chord and she pick it up in her mouth, turned around and walked back in the yard. She came from wide open space of grass and fields. I live in the city, not too noisy, but sidewalks and cars line the street. My plan was to walk with her every morning to my gym that is pet friendly and I can't get her past the neighbors house! Help!