Desensitizing fear aggression is a challenge in patience and stick to it-ness! Your attitude is paramount to your dog's success.
Part of the trick is to place the dog IN situations that may stimulate the problem...but then not to such a degree that the dog looses all control and ability to listen to YOU.
Also, using some really PRIME goodies helps. The set up goes like this...Armed with your PRIME GOODIES...(like boiled chicken livers, or some beef or chicken MEAT, or Human grade Beef or Turkey Jerky...whatever you use MUST CAPTURE YOUR DOG'S ATTENTION and should be cut into VERY tiny bits...you may give one piece at a time for "low level" threats...but then need to bump up the reward to a "jack pot" of several pieces fed quickly to claim the pup's full attention.
The goal is a reaction inducing person/dog (whatever causes your dog to react) comes into view...NOT NEAR YOU AT ALL...just enough to be seen by your dog...YOU start by saying nothing...BUT YOU HAVE THE TREAT IN HAND AS AS YOUR PUP SEES THE "SCARY THING" YOU DO YOUR BEST TO POP THE TREAT IN TO (hopefully) the open and willing MOUTH of your dog. You are REWARDING THE DOG for NOT REACTING.
You first must find out how close or far away the "scary thing" needs to be so that your dog DOES NOT REACT...and you reward for...NO REACTION.
The scary thing comes slightly closer, REWARD AGAIN with a MINI JACKPOT! NO REWARDS for barking at all. What will help this go even easier is if you have TRAINED this pup to SIT, LAY DOWN, STAY on command...the reason for this is that you can use theses TRAINED BEHAVIORS to REDIRECT your dog when he starts to REACT to the scary thing. He is doing something you DON'T want him to do, so you redirect him to do something ACCEPTABLE for him to do and immediately reward him for doing A CORRECT behavior....make sense?
I suspect he is nipping and becoming overly stimulated when you come home, because you have ALLOWED he to behave this way, and haven't stopped him by teaching him the acceptable behaviors...you need to STOP REACTING TO HIM..CUT HIM OFF FROM WHAT HE WANTS FROM YOU, which is immediate attention!
Again, he must learn his basic obedience in order to learn how to become a well behaved dog...he has no clue, except to do as he wants...you have to put the time in to teaching him...with positive rewards like TREAT AND PRAISE for every single CORRECT behavior he learns to do.
Right off the bat he has to learn to SIT, to LAY DOWN, OFF or Down or OFF OF ME...so he doesn't continue jumping up...unless he is sitting, he doesn't get petted...and you need to bend down to him to pet him otherwise it makes sense from his perspective to JUMP UP to reach you.
The nipping too is an unfortunate situation that YOU, or whoever spent time with him as a younger puppy ALLOWED TO HAPPEN, by not stopping it cold. When a young puppy nips, immediately you place a puppy toy IN the puppy's mouth...(redirecting from the unacceptable YOU to the acceptable TOY). IF the puppy prefers to nip YOU, YOU YIP AS IF IN PAIN...not too hard to do with those sharp puppy teeth eh?...AND THE GAME ENDS...YOU GET UP, IGNORE THE PUPPY, AND REMOVE YOURSELF TOTALLY. (No yelling no smacking needed) This NON-verbal communication is understandable by puppies and dogs...it is what their own Mom Dog would do...as the pups get older Mom Dog is LESS tolerant and may nip the buggers right back...as for US...simply ending the game works too!
NOTHING IN LIFE IS FREE (NILIF) would be a really good idea for this puppy right now...but you have to train him so he can DO the acceptable behaviors first!!! With NILIF...he has to DO an acceptable behavior to EARN what he wants...lovies, going for a walk, getting his lead attached...DINNER, food rewards, praise...he has to DO something correctly that YOU ask him to do...
All of this training will also give him a lot to think about besides acting aggressive, or spastic. It will also BUILD his self esteem (and yours too!).
I don't know that he even has Separation Anxiety...does he trash the house or his crate when you are gone? Chew things he should not, lick excessively on anything like a leg, paw, pillow?? Do neighbors claim he yowls and yips almost the entire time you are away?
I suspect this little guy is well on the way to developing delusions of grander about himself and his status in your relationship...he would not be the first dog to believe that manipulating the humans is s fun and profitable way to get what he wants!
He is NOT trying to be a BAD dog...like every living creature, he simply wants what he wants and this way seems to have been working well for him...he needs some NEW WAYS to earn what he wants...then you can work on the possible fear aggression..(was he temperament tested by someone qualified to do so or are you assuming he is fear aggressive?) He may well be heading in that direction...but YOU can change this if you put the time into it.
If you decide to in list the help of a professional trainer...ONLY USE ONE WHO TRAINS WITH POSITIVE REINFORCEMENT (+R)...keep it all positive and he will learn to shine!
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