for some reason there are dogs who just don't want to potty while on a leash..
While I don't like them, how about getting a flexi lead, or a long rope?
I had a female whom I did alot of trialing with, that dang dog would NOT go while on leash, she would hold it for a week if she had a leash on,,I got a flexi and / or offleash, no problem
But like I said, I hate flexi's
I ended up getting a 10 ft leash, and that worked, so after a time, I' shortened it to a six footer , she finally got the idea that it was ok to go with a 6 ft leash on
Now Masi, that girl will go anywhere, anytime, even if I had a 2 ft leash on her, she has no shame whatsoever