I don't have an answer for you on how to get them to get along but isn't Ruger supposed to become a service dog for you at some point? If you give up on trying to get Remington to accept Ruger that would not further your efforts in the service dog arena. Sounds like he wouldn't want any other dog around. Hopefully someone will give you some good ideas, I'm thinking some of the breeders or people who have fostered a lot would be good resources as well as Ruger's breeder. You've had him for what, less than a week? Let's see if someone has some good ideas before returning him to his breeder quite so soon. Keep them separated, maybe by a baby gate where they can see each other but not get to each other. You'll have to protect Ruger from Remington's advances for right now, Ruger's too small to protect himself. Be sure to give Remington plenty of attention as well as the new puppy.