You are now a trained team, but then it goes wrong. Well, that can happen. When you see it happen, bring your puppy outside immediately. To reduce the mess, but also for the routine. Don’t get mad at the puppy as this can backfire. Completely ignore the incident, because talking kindly can feel like a reward. Make sure your pup isn’t around when cleaning up and use a cleaner that really removes all odors. If a light urine smell remains, it is very attractive for your puppy to urinate in that place again.