Cody might be marking his territory since the new pup is there.

How well do they get along? Is Cody neutered? How long has the new puppy been in the house?

Hopefully once Cody gets used to Casey, he will stop. I would keep an eye on him and catch him in the act. When he starts to do it, clap your hands and take him outside.

If its not territorial marking, I would just start all over on the potty training.