Nipping friends and strangers

Question
I have a 2 1/2 neutered mail Aussie that I adopted from the pound when he was 1 year old. Since he turned 2, he has been nipping people (unprovoked)who come into the house (not our immediate family)and when they come into the yard. He gets very wound up when a strange car pulls into the driveway or someone walks up the driveway. He has broken skin a couple of times. I had him in training classes and he was leash aggressive towards other dogs (he is fine when I've seen dogs come into the yard). The leash walking/dog aggression is not very problematic now, since we worked with a private trainer for a couple sessions. This nipping people started about 6 months ago. Before that he was fine with guests. We have an invisible fence that prevents him from going on the driveway but yesterday he went as close as he dared and got my son's friend. This dog is very loving and gentle with us and gets along well with our other Aussie, a 3 year old spayed female, we've had since she was 8 weeks old. I don't think a rescue organization would take my male with his history of nipping and my husband is losing patience with the dog and worried about being sued. Hope you can help.

Answer
Original stockdog type Aussies are known for their guardiness as well as their herdiness, and, especially if the dog was not extremely well socialized as a very young puppy (and sometimes, even if he was), the tendency toward guardiness can be exacerbated.  The reason he is doing this now is probably related to one of two things.  He is at the age of social maturity.  That's the age when dogs determine just who belongs to their pack, and who doesn't, and is often when this guardy behavior becomes more pronounced.  So, the dog that barked before, as a puppy, to drive a "threat" off is now, as an adult, "enforcing" his threat with a well placed nip.  Also, the electric fence may be contributing to this.  These guardy type dogs are best contained in solid fencing that does not allow either sight or contact with guests.  In electric fence, if the dog perceives the threat as great enough (he thinks his family is in danger) he may leave the boundary regardless of the shock, especially after repeatedly being "teased" by strangers - not that they are actively teasing him, but from the dog's perspective, his fuss makes the joggers go away (down the road) or the guests disappear (into the house or their cars) and so when a person comes too close and *doesn't* disappear, he thinks he must escalate the threat to make them do so.  That's why blocking these dogs' visual access is important.
You are correct that rescues would not be likely to take him, although you could check with ARPH if the nipping has not been severe.  As the owner of a guardy dog, I can tell you that I simply contain my dog in a solid fence or I crate or kennel her away from guests.  The way to keep guests safe is to keep the dog safe.  While there are protocols that can alter this behavior, they are lengthy and require many "volunteers".  Dr. Nicholas Dodman has one, and another good one is by Dr. Karen Overall.  But, if you do not have the time or number of volunteers, the best solution is to contain the dog in a way that does not allow him to threaten anyone.  This behavior is one reason why reputable Aussie breeders place their puppies carefully and tell potential owners that this isn't the breed for everyone.  I hope that you will be able to manage your dog successfully now, and have him as a loyal member of your family for years to come.