Rescued Papillon is Very Aggressive

Question
We (me and my two sons, ages 11 and 14) adopted a Papillon (approximately 1-year-old, named Pippin) from the Humane Society a little over a week ago.  While visiting Pippin at the Humane Society, he was friendly, although a bit timid with us (very playful and happy with the staff).  He didn't react at all to the other people there visiting other dogs and cats.  In fact, he barely reacted to the other animals at all.  Pippin did nip at my younger son the first time he went to pet him, which we agreed at the time had more to do with David's approach than the dog.  The staff assured us that Pippin's temperament had been thoroughly tested and their only caution was to avoid small children.  They did not know anything of his history as he had been found as a stray.  Pippin seemed happy to leave with us, and he was very well-behaved on the trip home (about one hour in the car).  We let him explore our house a bit (only on lead, never on his own), and then showed him his crate.  We sat on the floor with him and played for about an hour until Pippin started to act a bit tired, so we put him in his crate.  At this point, we were all very pleased with the new member of the family.  At supper time, we fed him while we ate then took him outside, then back to the living room to sit while we watched TV.  My youngest son, David, was still in the kitchen finishing his supper.  When he was done, he walked out to the living room (no abrupt movements, loud voice or any other danger signs) to talk to his brother and the dog IMMEDIATELY lunged at him, growling and barking in a very frightening manner.  David screamed and ran (and I can't say that I could blame him for the dog's behavior was incredibly threatening).  We were fortunate that the dog had not been allowed off lead and that Ryan had a tight hold on the leash at the time of the attack.  

Since that night, we have worked diligently to socialize the dog, and he and David are now well-bonded.  We put an old shirt of David's in Pippin's crate, had David routinely walk by the dog without showing any real interest, and finally had David stand his ground against the dog's aggression, and now David is as responsible for feeding and potty breaks as Ryan and I are.  

My concern at this point is that Pippin continues to show this same level of aggression to anyone outside of our family (just the three of us).  We have tried to limit outside interactions, but the few people who have been exposed to him find this behavior very frightening and intimidating.  They have done well to hold their own, but it is clear that they have little faith in the strength of the leash.  Additionally, he responds more strongly to men than women, showing extreme aggression the minute a man is in sight and not stopping until well after the man is out of the room.  

We are supposed to go out of town for 3 days next week, and my neighbor was willing to take care of the dog for this time period but is now frightened of him (and she has three dogs of her own, never had a problem with fearing dogs).  Taking him with us is not an option (my brother's three very small, very active, rather naughty children will be staying in the same cabin with us).  Do I take him to a kennel and hope that he does not bite anyone?  Do you have any tips for socializing him enough that my neighbor can handle him for three days?  Do I even have any hope that this dog will ever be socialized?  How do I know if this aggression is part of his nature and he will never be trusted?  We are willing to work with him, and both of the boys and I have been reading books and watching training videos for months in preparation for adopting and much more in depth in the last week as we are dealing with this behavior.  Obedience classes may not be possible, as the nearest classes are 45 minutes away, and this current level of aggression does not bode well for stepping into a room full of strangers and strange dogs, especially when it is almost a guarantee that those dogs will be much larger than this tiny 8-pound dog.  However, the longer we work with this dog, the more my sons become attached to him (he really is a lovely little dog when all aggression triggers are eliminated).  I don't want them to go through major heartache if this dog can never be rehabilitated, and for that matter, I don't know how long to work at this before we determine that he can't be socialized.  We can't put our lives on hold forever, and it is impossible to ban all visitors from my home from now until eternity, and I absolutely do not want the lawsuit associated with a dog bite (and yes, he does bite, luckily only caught the fabric of my neighbor's jeans and not any skin, and no, she did not do anything to provoke him).  

Any tips or suggestions would be greatly appreciated.  Do we keep trying or do we take him back to the Humane Society?  Thanks for your help!

Answer
Well what you can do to get him used to the neighbor is to have her come over and give him treats,but ONLY when he is not being aggressive,as that would encourage that problem

A kennel is also a good alternative-I do work in a kennel myself and do see a lot of aggressive dogs and in most kennels staff are well trained,my main concern with that,as I even tell some potential customers with dogs like that,is that SOMETIMES it make them more fearful when they leave,although it is not always the case

Something you might want to look in to are trainers that actually come to your house instead of you going to them,as with dogs like yours it is actually better for a trainer to come in,so that he/she can see the problems you are having with your dog-and vets will often have there contacts,and thats a good way for a trainer to address the problems you are having with the dog at home

I think this dog can be worked on-he just needs a lot of time,and it seems like you are willing to do that