Dog wont go potty and stops moving on walks?

First, because it sounds like this dog is experiencing moderate or greater separation anxiety, let me caution you to use tactics in effort to try to “convince” the dog to go with you - A dog like this can sometimes back out of a harness (leaving the walker holding a leash attached to a harness with no dog inside it) or pull real hard with such force that pulls it right out of a walker’s hand and bolt.

If this is a dog that likes squeaky toys, one way might be to use the squeaky toy to get the dogs attention and try to make it like a game. If this dog knows the command “ look at me” you can use that intermittently too. If this is a very small dog that you can carry, you might have better luck carrying it away from home and then letting it walk back towards home. If this dog is allowed treats, you might try taking them on the walk and breaking off tiny pieces given frequently for walking nicely with you. If you can contact your friend, You could ask if they have any tips that will motivate their dog.

Usually I would recommend that a walker continues walking as close to the same route as possible as what the dog normally walks with the owner when possible.

I agree with Deb A.'s suggestions for getting the dog's attention and making it a game using a squeaky toy or the command "look at me". Another strategy to try is using high-value treats that the dog really loves to motivate it to follow you on the walk.

In addition, I would suggest gradually desensitizing the dog to being away from its owner by starting with short walks and gradually increasing the duration and distance over time. It may also be helpful to practice some obedience training with the dog to build trust and establish a stronger bond between you and the dog.

Finally, if the dog's behavior continues to be a problem, it may be worth discussing with your friend and possibly even consulting a professional dog trainer or behaviorist for further guidance.