Wont go potty while on leash

Question
Dear Cassie,

This is my first time to this website and so far am impressed with the wealth of information.  While I could have chosen to write to any of the experts, I guess I chose you because of your profile.  I agree with and utilize dog psychology as well.  Therefore, I am anxious to read your response.  My issue is that my dog doesn't seem to EVER go to the bathroom if on a lead or any kind of tie-out.  Collar on is ok, but nothing attached to it.  Let me give you a little background in case it might help guide your response.

I rescued Risa, a Louisiana Catahoula Leopard Dog mix (with Australian Kelpie, maybe?), 16 days ago from the Humane Society.  She is almost 14 months old.  She was very submissive when I adopted her; still is, but is not as shy now as she's becoming acclimated to her new home and pack leader.  She's also rather intelligent and highly trainable.  I already have her obeying the following commands (some a little better than others so far): come, sit, down, stay, roll over, (go to your) spot -> her special carpet in great room, bed (she goes into her crate), gee (turn right), haw (turn left), and potty (but not on a leash!).  I'm proud of our progress so far.  Furthermore, she is doing well with socializing with strangers (young and adult) and with other dogs.  One last note, I have a cat and the two are coexisting fairly well.  The cat is still the timid one, but Risa does not "go after" her.  I also keep a close eye on their proximity to each other and monitor their interactions.  We're taking it slowly and it seems to be ok.  Hopefully the cat, Jigs, will feel welcome to come downstairs again soon.

So, what can you suggest for me to get Risa to go potty while on a leash or while on a tie-out in the backyard?  She will go in the backyard, but only when she's "free."  Thank you in advance for your time and your response.

Cole

Answer
Hello Cole,

   I'm sorry to admit that this is one of the most uncommon questions I have recieved, and I really don't have any clue how to solve this problem. I do believe I know what is causing it, however. You mentioned that your dog is very submissive. Your dog is probably submissive to other people and dogs as well, right? Well when a dog relieves itself, it is marking it's territory, as you may know. If your dog is as submissive as you say, then it probably doesn't want to be picking a fight with another dog by saying that this is it's land. I wish I had an idea of how to fix this! Sorry! It's just the personality of your dog...maybe in time, as you said she was just warming up to her new home.