Sorry that it's been a few days since I've posted.  Things are a mixed bag right now that I'm trying to deal with it.

Also, sorry for the incoming wall of text and ranting/unfocused rambling.

Dozer is doing well, moving around as well as can be expected for just under 2 weeks post surgery.  We're gonna hear they got the biopsy results back soon I imagine and then he'll be getting his stitches out either this weekend or next weekend, depending on the biopsy results and consultation timing.

The bad that we're dealing with is one of the other dogs in the house.  We have a Basset Hound that without sugar coating it, is a terrible dog.  Part of it is failure of my girlfriend to deal with issues he had when younger that have been allowed to fester to the point where he's at now. He has spent the better part of 8 years being the alpha personality in the house and acts accordingly.  It's normally minor things like insisting on marking his territory when the other dogs are out for bathroom breaks anywhere they go to the bathroom, etc.  Since I've been living there though, his behaviors have steered to a significantly more aggressive nature.  Likely due to his feeling of displacement in the hierarchy. 

He's quick to be aggressive with me over minor things.  Example:  I went to bed later one night last week and he was lying in my spot in bed and when I woke him up to move him, he started growling and barking at me which eventually escalated to snarling after I repeated my insistence.  I had to eventually just move him by the scruff of his neck all the while he was growling at me.

I've been with my GF for between a year and a year and a half and we have only been living together since September.

However, on to what I consider the actual problem:  Due to the nature of what's required for post surgery care like extra attention and being overly fussy about/with Dozer, I think he's feeling sort of ostracized, even though we are providing him with about the same amount of attention as pre surgery. However, the third dog, Elvis it should be noted is handling things just fine.

He's one of those dogs who gets angry/spiteful if he perceives things as being "unequal".  With food, attention, sleeping conditions.  Anything really.  Resource hoarding would be a major problem with him if we allowed it to happen.

Anyway, after about 2 days of Dozer being home, he started being aggressive with Dozer only.  He has yet to bite him or anything that severe.  Initially he was growling/snarling at Dozer about 75% of the time when he's moving around the apartment and randomly when Dozer was lying in his bed.  The frequency he's doing it has subsided to maybe 10-25% of the time now but I think it's because he's accomplished his goal of intimidation.  Dozer is noticeably uncomfortable when Arnold is in the same room or enters the room.  He pins his ears back and only looks at the floor.  He won't come into rooms if he's in there even though you can tell he wants to.  On more than one occasion, I've been on the floor with Dozer for whatever reason and Arnold will come up to him and Dozer starts shaking/trembling.

Needless to say, this is a major problem.  I have zero tolerance for an aggressive/violent dog and this would have been dealt with sternly and quickly the first time it happened (she said it didn't start until he had lived with her for 3-4 years).  I can't figure out how to break him since he's almost 10 years old and has been this way for nearly 6 years.  I've tried being patient, putting myself between them and speaking to him in a calm and even voice (at which point his anger and aggression gets redirected at me, which I guess is the better option of the two for the time being).  He was abused as a puppy and was in bad shape when she adopted him so if you get physical with him, it understandably makes him worse.  That's not a normal reflex for me in the first place but it's just that positive reinforcement doesn't work for him, patience doesn't work, physical restraint/discipline doesn't work, repetitive correction to establish new habits doesn't work.  Simply put, he seems untrainable. 

She keeps chalking it up to him dealing with things being different but from watching it, it appears to be predatory behavior from my perspective, especially as I've seen him more than once sneak up behind Dozer and start growling with teeth bared/hair on his back standing up like he was planning on attacking.  It seems predatory in that he sees an injured dog that is larger than him and only then becomes aggressive after living together peacefully/happily for 9 years.

I'm going to look into behavioral specialists and if it doesn't subside, we may have to consider that he can't stay with us.  We certainly can't let him create an environment of fear and intimidation for Dozer coupled with the constant stress which will almost certainly shorten his lifespan.  The idea of getting rid of a dog isn't appealing to me (even less so to her) but at some point it becomes the only viable option.  I hope that isn't what we're looking at.  It's also way too early to make that call so at least that fact gives me some hope.

If he can find a house where he'd be the only pet, it may be optimal for his mental health in the long term.  Obviously the post surgery reality is causing him distress.

I'm gonna go through the steps needed though to try to get him comfortable again as I certainly want this to only be the last option.

Sorry for the ranting/rambling.  I guess I'm just kinda using this space to get my head around it all.