Hi!
I've been a trainer for a fair bit and my current specialty is difficult dogs. Without hearing more about what's going on (and preferably seeing it, of course! LOL) it's hard to say, but the description sounds like your typical confident puppy. The sitting down thing is actually a sign of "I'm not quite sure about you", which is normal behavior for a pup of that age. It would be normal for him to do this up to around 18-24 months, as he matures, though you should see less of it over time and as he gains good doggie social skills.
I'd have him hang around as many dogs as possible, off lead and preferably off collar, to help him learn to be a good grown male dog. Be aware that most adults will take him down A LOT after his "puppy license" goes away, usually around 8-10 mos. This means that the bulls*** stupid puppy stuff that he does will be tolerated until he's considered an adolescent, then older females (and some males) will roll hime and generally nail his ass to the ground frequently. There may be a lot of spit and screaming, mostly his, but no one will get hurt -- and it's vital that you let it happen! The more noise, the less damage is being done; it's the silent, quiet snarling that means trouble. A "yarp-snap-growl-rowf" means "knock it off, you idiot teenage boy! Mind your manners!" It's over in less than a minute, usually less than 20 seconds.
I often tell people that teen boy dogs spend about half their lives upside down screaming pitifully under some older bitch. I quietly applaud the older bitch, myself; she can teach him manners much more efficiently than I can. It's her first language, and I'm just limping along speaking bad Dog.
So let him learn with older bitches and mature males and age peers and mellow teens. You say "most of the time he walks away with no harm" -- does this mean that some dog has punctured your puppy? If so, don't let that dog near him again; that dog is not quite right in the head. Adults don't hurt puppies! Oh, they scream and yell at them and jump up and down on them, but they don't hurt them, just discipline. If all you are seeing is spit and a puppy who behaves himself for a few minutes, shaking himself off after he gets up, that is normal behavior and you should politely congratulate the dog who taught him some manners.
I would clicker train him (operant conditioning with or without an actual clicker, but definitely with a marker and paycheck (a teeny treat)) because if he's "dominant" (not a very accurate word, but o well), force training will bring out the worst in him. With operancy, you gain a partner and build a relationship on trust and responsibility from both ends of the lead. More efficient and works better!
Do NOT show a treat and beg for performance!!!! That's called a bribe and it's why so many dogs won't work unless food is shown. I could go into it more, but this post is quite long enough. email for details if you're interested.
Short form, your pup sounds like a winner. Good dog, good brain, perfectly normal. Glad to hear that tail is up a lot; makes training easier!
Katherine Bryce
The Family Dog
Santa Fe NM USA
