Oh, Boy. Have I Ever Been There. But I won in The End
I bought a Giant German Shepherd. He's tough as all get out too. And, we had on heck of a time trying to bring him around. It took at least two years and we're not 100% of the way to where we want to be now, just weeks from his 3rd birthday.
It sounds like you've allowed some pretty bad habits to develop. They're going to be hard to break now that he's so much larger than he was as a puppy.
Let's just start with pulling. Get a prong collar, back it up with a choke collar and without anger let that dog feel your power right from the beginning of the walk. With mine still takes a couple of stiff jerks as soon as we leave the house to get him to realize that I mean business about no pulling.
At the beginning of the walk on a short leash stand in front of the dog and make him sit patiently using whatever level of correction you must. It's the only way to set the walk up right. Then start with short walks and terminate them long before he wants to, again, to demonstrate that you control the walk and not him.
Importantly, when it's over find something to praise the dog about. And, then switch from the menacing and demanding to the loving and tender.
This dual approach finally worked with mine.
Someone else can take up reactive behavior towards other dogs. Personally, I think dog parks are the worst possible option right now.
Last edited by Longfisher; 10-09-2015 at 09:17 PM.