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About a year ago, my parents rescued Moose. At the time, we thought he was older than he was. Turns out, he was a VERY large puppy. Of course, he was hyper and excited, but since has not calmed down....at all! He was neutered. He has some good days, but the bad days are terrible. He finally got the house training down, but he still gets over excited and has separation anxiety with a tendencies to destroy things. They also have a 6 year old Jack and Pit Bull mix female. She is a sweetheart, but only takes so much of Moose's antics. I am not sure if it's playing that goes too far or if it's a dominance thing. He is caged when no one is home, but he lunges at visitors coming through the door and just takes forever to calm down. They are using a shock collar mainly because of his sheer size. We know he needs more exercise, but being over 100lbs already and not good on a leash, that is virtually impossible. They also use calming treats...sometimes they help, other times, you wouldn't know it. They really, really don't want to re-home him and if need be, it would be a good home, but they really do love him...I am sure some of the behaviors might be outgrown, but the aggression things scares them. Any thoughts would be appreciated!
Get rid of the shock collar. Horrible for any dog with anxiety and not particularly good for most dogs for most owners. Way too easy to shock at the wrong moment and punish a desired behavior or shock during a moment of fear or stress and make it worse.
Giant puppies/youngins are still just young dogs. Just because the body is large does not mean the brain has matured and caught up. Lounging and barking at guests does not always mean aggression, it might but it can also commonly mean overexcitement.
Work a lot using treats and positive reinforcement for "four on the floor" -- all paws on the ground before any attention. Contain him when new people arrive, work him behind a door or baby gate with treats to associate guests with sitting nicely and then getting his treat.
Exercise mentally as much as possible. Training tricks, food from a puzzle toy. Look into "Nothing In Life Is Free" (NILIF) as it may provide the kind of structure that your parents would prefer.
Very much agree to ditch the shock collar. That could very easily turn an excitement problem (YAY NEW PEOPLE) into a fear problem (new people HURT! I have to scare them away). A bite in much more likely to happen in the latter than the former. Look into a well-fitting front-clip harness or a head halter instead. Halters might require some careful introduction with lots of rewards so the dog is comfortable wearing one, but there's a lot of info out there on how to do that, and we can help where we can. You can also keep him crated or behind a barrier until he's calmed down before you introduce him to visitors - if he has to meet them at all.
I'd suggest looking up a qualified, reward-based trainer in your area. Not someone who uses physical punishment or talks about "being the alpha" or "dominating" the dog - these are outdated concepts that have been proven false, and so are no longer used by good trainers who keep up to date on how we understand how dogs think and learn. With such a large dog, I feel you'd really benefit from some one-on-one, in person guidance on how to handle him.