Everyone here has givin good advise I just thought I would add something about the flexi leash. I know someone who had one and the dog pulled it out of her hand. THe handle part hit the dog in the butt and scared him, for a long time he didnt want to walk on a leash, and was nervouse for an even longer time when back on the leash. He kept looking behind him to see if something was going to hit him in the butt again. So if you have a dog that is already scared of leashes I wouldnt use a flexi.
This was actually what was suggested to me for Smudge. Smudge already knew how to walk on leash before he went to class, but she told me getting a really long leash and putting it around my wasit was an exellent way for Smudge to learn to walk with me "off leash".

Well you wouldn't need to worry about her running off. 