We faced the same issue introducing the Mal pup to our aging Eastern European GSD. For the most part they get along very well now, but it was precarious for a bit. The Pup is relentless with her pestering the big dog who is literally twice her weight and size. The pup is just a shade under sixty pounds and I doubt she will get any bigger. The play got a bit intense the other day and the pup turned on the “Mal switch” and tagged Hemi about three times on both sides of the head before Hemi even knew what was going on! The pup is deadly fast.