I would not use a retractable leash while training. Once your dog is pretty good at leash walking and knows your commands, then it'd be okay to use it again. When I take my dogs for a walk, I let them sniff anywhere as long as my arm holding the leash can hang comfortably by my side. If they start to pull then I just stop walking. Then they know they have to come back to me and sit before we start again. An important thing to do is not let the dog get anywhere when she pulls. If she pulls and gets to her destination, then she is being rewarded. Good luck