What does this behavior mean?

My GSD/ACD is still a teenager at 15 months and going through some behavior changes. I rescued him when he was 3 months, and he has a questionable past of abuse from people and other dogs. He is fearful, and I was looking at dog behavior webpages tonight when I found this (use this page as reference for the behavior I describe if you don't know what it means).

http://www.buzzle.com/editorials/3-11-2005-66974.asp

When we are on walks and meet other dogs we encounter, he displays raised hackles, fearful threats upon the other dog approaching, when they sniff a lot of the time he does the T-Bone. Our last walk we encounter a large poodle, he did all the behavior as described as above, and while he was doing the "t-bone" he did another thing I read about called the "half-moon eye" (white of the eye in a half-moon shape - where it looks like they want to bite!). We seperated them at this point.

It's pretty obvious he is scared, but i've never seen a scared dog do the t-bone while displaying the signs listed above of being scared. That's what gets me. Also, when people or children try to approch him he does the raised hackles and fearful threats posture, and will back up if approached. We have done normal and advanced training classes.

I'm just looking for opinions and advice. This summer he did bite a groomer who was trying to trim his nails after she trapped him and was reaching down for his paw. Other than that, he hasn't shown any other real signs of aggression towards strangers. Is it feasible to consider the fact that he could bite a stranger or child if they approached him too fast, or forced themselves upon him? Also, should I still let people and other dogs interact in the hopes that he will get better when he realizes everyone isn't out to get him (although he did have lots of socialization in class and it doesn't seem like it did much, because he is even more reserved around people now). Sorry for typing so much, but this is a pretty serious issue to me and appreciate any advice or opinions you have to offer!! Thank you!

The URL doesn't want to copy correctly, so i'll just copy and paste the terms I used to describe his behavior. Most of you know what this means, but just in case.
Raised Hackles-
Hackles are the hair on the neck and back that are raised involuntarily in anger or flight. Fearful Threats-
A slinky low posture with the tail between the legs and the ears rotated back to one side. T-Bone-
Dominate gesture of placing the head over the shoulders of another dog.

It sounds like your dog is not sure how to handle social situations with other dogs and possibly needs some socialization or more training to teach him how to handle his stress. Some dogs need "jobs" when meeting dogs or people. I have a friend who's dog sits when it encounters other dogs or people, this gives the dog something to do and gets him past the ackward meeting.
I checked out the website you listed.
You don't say how your dog did in the classes you have taken.
A really great book you might want to look into is
http://www.clickertraining.com/store/
it gives you a postive way to help your dog through this diffcult time.
Good luck

He is a very smart dog so he did excellent with his training, but didn't care to play with the other dogs at all. Thanks for your response.

pcarfan,

I agree with ginagt that your dog may need more socialization. Some dogs are naturally more fearful than others and if your dog was abused at some time this could be a factor too.
My second dog came from a similar situation- we adopted her as a pup but not before she had been abused, and also she has a naturally shy disposition- and so it has taken quite a bit of deliberate socialization to get her where she is today.
What we did was introduce her to as many dogs and people as possible (in a non-threatening, controlled way) while she was still a pup and I also try to do so while she's an adult too by taking her on walks where she can meet new faces. She's done pretty well but she is still wary of kids; she will leave them alone but doesn't particularly like them until she has been introduced to them several times.
I'd suggest taking a look at some books or articles about how to socialize an adult dog. Here's a brief one:
http://dogs.about.com/library/topics/bltips006b.htm
I hope that helps. Good luck to you and your pup!

Pembroke_Corgi

MHO
Your dog is an adolescent as is going through behavior
changes. Unfortunately your dog had a rough beginning.
Socializing is so important, needs to begin early,
and to be controlled especially with a dog that has a bad past.
Confident building, trust and happy situations are important.
If already a problem exists and the dog experiences more bad experiences in life,
It only makes the dogs behavior more
negatively enforced I would think.

I would seek out a excellent behaviorist to evaluate and
help you with your dog so you have the tools
to continue with future situations/behavior training.

Your dog sounds like he could be a potential fear biter.

At this moment,
I personally would keep socializing but under control situations
under the guidance of a behaviorist/trainer.
Even though you might need to work with him through-out
his life-time, it will be easier for you once you have the tools/
know what your dogs limits are.

Just my 2 cents :)