How do I train an older puppy? ?

My puppy is a year old and he is impossible to potty train! Its very hard to punish him because I never catch him in the act. I know if I punish him after, he will have no clue why. I JUST caught him red handed hiking his leg in the hallway. I stuck his nose in it, not forcefully, and told him "No!".. I then sat with him outside for 5 minutes. He just stared at me with puppy eyes. (so hard to be mad at him.) Now he is in his crate away from me.. And whimpering. Is this an okay method? And how long should he be isolated? It's getting to the point where my adult dog, 9 years old and completely house trained is starting to follow behind him and pee where he does. Both males, obviously.. But they are also both fixed! Ugh!! Help me! I'm fixing to move to a large apartment and I'm worried to death about them peeing everywhere! The baby just doesn't get it at all! OH, and.. I have a doggy door they are all completely capable of using. I spend lots of time working with him. I take them out all day and wait.. Jasper NEVER uses the potty when I take him. I'm not being lazy, but I can't spend 30 minutes every hour of the day waiting for him to go!