how can i stop my rescued 18 month old gsd from lunging & Barking in fear?

Wow! I hope Tommy S. never gets "damaged". No one will want him, either! Your poor dog is obviously traumatized. That being said, you will need to do alot of things differently than with a normal dog right now. At this point, you need to realize that your dog could be DANGEROUS. Get him into obedience training asap-and you may have to do this with an individual trainer, as he may not do well in a room with other dogs and people. In addition to the abuse he suffered, he will go through a period of distrust of everything around him because he is not comfortable in his new home yet. When a dog doesn't feel safe, aggression can come out easily. In order for your dog to feel safe, he needs to know that you are in control of him and the household, so that way he doesn't have to worry about anything and won't feel it necessary to do your job for you.Some tips on handling abused animals-don't let people come right up to him standing up. This can be taken as threatening behavior by a dog. Don't pull his collar to lead him anywhere. Use a leash. Don't let anyone in the house raise their voices for awhile. Always have your family members let the dog come to them first.The dog needs to make the first move here. Introduce him to new things slowly, so he has an opportunity to tell you he doesn't want to do that right now-you can always try something tomorrow!I also wouldn't suggest taking him outside in public much either, until you get him obedience trained. Right now you will have no idea what he might do.Don't expect too much too fast. Your dog is in a very scary place right now, and it may take him quite some time to get used to his new home. You will love it the day he realizes he is home and he relaxes for the first time!Good luck and thanks for taking him on! We need more people like you out there!Resource: Five months of obedience training with an abused Australian Cattle Dog

i have 3 gsd now but Ive had different shepherds throughout my life as my dad breeds them so i think i know the breed well enough to offer you advice unlike some. Ive been in your shoes i have a big boy now called "soldier" he is a great dog but i got him as a rescue when he was a pup and boy does he have some issues, even now with all the training he has had he can still be a royal pain in the arse but that's shepherds for you, they can and often do suffer from nervous aggression its common in the breed and you need to get a firm hold of him (mentally) he needs to know who's the boss it takes time and Patience and i suggest a professional trainer is your only option as hes age and past experiences go against you solving his problem this is not saying you cant start basic training as it were but this can be a complex area and cant be solved by posting an answer here , it needs professional attention especially him being a shepherd, because if it it isn't things can and probably will go from bad to worse. seek advice from your vet as to a good trainer in your area don't for god sake ring some animal behaviourist out of the paper without a good recommendation as these people are a waste of space. remember he is a shepherd the most intelligent breed in the world he and you just need pointing in the right direction which given some professional advice and guidance wont be a problem. good luck