Grabbing by the Scruff - Bad? (Couple Questions)
So I have a very stubborn GSD pup and a very stubborn roommate. My roommate consistently tries to get my pup (only been in home for 4-5 weeks) to co-exist peacefully with his cat. However his cat is 9 years old and my pup only 8 months... The pup very obviously just tries to play with the cat but the cat wants no part of it. Since we live in a small apartment the cat gets cornered very quickly and starts trying to attack the dog, hisses, etc etc. The dog in turn freaks out, barks, breaks stuff and keeps going back to the cat... Since I don't want my dog or his cat getting hurt I told him to stop for now until the dog gets more comfortable in the house at least. However now the dog knows when my roommate gets home the door to the cat will be opened.
For a couple weeks my roommate was seemingly okay with keeping his door shut but now he won't. And the dog keeps trying to sneak/force his way into the room. He won't listen to no when he does this. He still doesn't quite see me as his master yet. Grabbing him by the collar only causes him to pull and fight his way back to the door. However if I grab him by the scruff and guide him away that works. I don't ever hurt him. He never yelps or barks however he has tried snapping at me once doing it but then stops.
Any suggestions on teaching a very stubborn dog boundaries? I'm his 4th owner in his 8 month life so I get why he is struggling to adjust and being very stubborn but could really use some tips for teaching him boundaries without establishing any sort of negative relationship in the process. I've read that mother dogs will move their pups by picking them up by their scruff which is what gave me the idea...