Hump him?

The adult is humping the puppy to show that he is dominant, what you have to do is first: Show your dog(adult) that YOU are the leader of the pack. Next time he humps the puppy pick a fight with him and win. He will get mad and come at you again, keep beating him until he submits. After he knows that you are the one in charge, you can Second: just yell at him when he humps the puppy and he will eventually stop. A lot of people don't like to be mean to their dogs, but just this one time you really have to kick his ass, it sounds bad but that is how dogs learn. Kick his ass = you are the pack leader = whatever you say goes. You say stop humping the puppy, he stops humping the puppy.

Pick a fight? no way...he already knows you are the leader by his behavior when you tell him no. A stern no and a spray in the face with cold water followed by pulling him off should work. Give it 2 weeks but be consistent.

Some of these answers are ALMOST or partly right. Although I have seen dogs hump, even when both or one has been spayed or neutered in a somewhat sexual, low or no dominance stress being part of the game, I do think this is related to Dominance over the puppy. Do you want the older dog to remain the top dog between the two of them...since OBVIOUSLY...YOU are real ALPHA OF THE HOUSE? After YOU one of them will be the next alpha in the canine line up. Who ever you want in "second command" FEED FIRST at each meal. Next to help your adult start to calm down, start training. Common sense says you WILL BE training the puppy so go ahead and give your adult a REFRESHER course using Positive Reinforcement, just like you will the pup. This helps to build both dogs confidence and self-esteem in addition to giving them good behaviors that you can call on when one or both of them starts to make an unacceptable decision on what they want to do. You are adding to your bag of tricks so that if they start to make a bad choice...you can GIVE THEM an acceptable behavior to do, and even REWARD THEM for doing it! You DO NOT NEED to kick his ass, or challenge him to a fight ever...that is about as wrong a thing to do as could be. You do need to remind him WHY FOLLOWING YOUR IDEAS results in totally awesome rewards and makes YOU the real pack leader of THE BOTH OF THEM! YOU are the source of ALL GOOD THINGS that they desire. REMIND the adult and teach the pup that this is true. If you start using negative training at this time, it is far more likely to result in your adult dog learning to HATE THAT PUPPY, because after it came along everything went to hell. You want them to get along peacefully right? You do not want to teach either dog that YOU are an angry and unpredictable person...right? You want them both to have total trust and confidence in you and in anything you tell them to do...so forget about the ass kicking bullchit..and keep it all positive so they KNOW YOU ARE THE BOSS... A TRUE ALPHA...RULES WITH BENEVOLENCE..THEY DO NOT START FIGHTS because they are 100% confident in themselves and their authority.