My sister and I own a house together and she has a 3.5 lb yorkie mix, he's a rescue and they estimate his age to be 14. He's small, frail, has cataracts so very limited vision in only one eye, and doesn't move fast due to joint problems. When I brought Delgado home at 9 weeks the rules were laid from day 1 that Nemo was not to be messed with. Anytime he got boisterous around him we corrected and redirected and we always supervised.
Keep the puppy on leash for the first little bit and always have toys and treats. You need to show the puppy that you're the best thing in his life, the more he looks to you the less he will pay attention to the other dog.
Now Delgado's older and he's learned respect, Nemo can be down on the floor wandering and Delgado will walk around him. Sometimes he forgets and bowls him over but if Nemo squawks Delgado immediately realizes what he's done and will back off. It takes time but it's worth it
Jasmine - Female Miniature Poodle - born Aug 15, 2010
Loker Delgado Von Stalworth - Male GSD - born Jan 26, 2012
Koda & Zazu - 6 year old male cats
Alex - Male Cocker Spaniel (rescue) - RIP Cuddlebug 2007-2010