My older dog is aggressive toward my younger dog; does anyone have any tricks?

[VenomQuill]

Hello! I am having some problems with my dogs fighting--in particular, one of my older dogs beating up our puppy. Mister's 10/11 years old neutered male, while Peanut is a year and a half intact male who will stay that way. Patches (13+, menopause) and Whitney (4, spayed) are our female dogs. I'll preface with: no one's being given away and Peanut's been here for over a year.

It's been happening for a while; Mister beats up on Peanut. Now, Mister is a sweet dog. He loves people, and though not the best with dogs after the initial greeting, he rarely snaps. Peanut is a very nervous dog who's scared of everything except dogs. Mister will attack Peanut fiercely. The first few times, it ended with a few tufts of fur missing and Mister's teeth and bones hurting from the exertion. Lately, there's been a few cuts. Mister won't let him upstairs where my and my siblings' bedrooms are and my mom's office. Mister, Patches, and Whitney all sleep with me. Peanut sleeps with my Mom downstairs. Everyone gathers safely in my mom's dog-themed office--even the cat!

In fact, just tonight he jumped up and attacked Peanut downstairs after growling at him over dinner. When told to go upstairs, he sulkily left and I tempted him to stay upstairs with a chew bone to be distracted with. Then he just jumped up and charged downstairs as if he was going to murder our sleeping puppy. Honestly, Peanut could take him. He's bigger, younger, stronger... and we're afraid that if Peanut gathers up the gall, he could seriously injure Mister.

We've been to dog therapists and, though they seem to be helping as it's less frequent to the point where I THOUGHT it was gone, they're still fighting. Peanut doesn't want to fight. Often he'll pee himself in submission and try to run away. Afterward, he'll try and be friendly to Mister with sniffing and experimental play. But Mister doesn't know how to quit. We know dominance fighting. But Mister doesn't stop, even when Peanut submitted. They know that Mom's the alpha, with me straight under her and no problems with dog assertiveness/aggression to us. We live in a household that can be neurotic at times, but it's not like it's a high-stress environment--quite the opposite with the daily playing, a big backyard, toys, treats, and fun meal times. None of them are deprived of attention or love.

Does anyone have any suggestions? Things we can try? We've had Peanut for about a year now, so it's not like he's new. We have scheduled feeding times with Mister getting his food before Peanut and training times where everyone gets treats for following commands.