Rosana,

Rex is a beautiful name for your new German Shepherd.

On, Rex's behavior, is there a way where you can copy your most recent posting about Rex's behavior and post it on the "Dog Behavior" Section of Dog of the day website? I think if you do that, more people will see your question about how to handle his reactive behavior towards other dogs and you'll get more answers/help that way. Maybe "need help-dog aggression" or something like that in the behavior section will get you more answers and some help on your question?

I have a hunch that Rex's macho 1st owner may not have done much (if any) training or socialization with Rex. Because if a pup starts growling and barking and over-reacting to another dog's presence, a responsible owner will take charge of that situation to teach the puppy that going into a sit and quiet command will get the dog a treat. And the owner would deliberately take the puppy into situations with other dogs (on leash and under control) to desensitize the pup to the presence of other dogs to teach the dog how to be a polite member of society.

Seeing that this 1st owner abandoned Rex and obviously never gave him toys (since Rex seems ignorant as to what to do with a toy), I highly doubt the owner taught him as a pup not to do this. Since no one ever taught Rex to not do this, he thinks his behavior is just fine and will keep at it unless he is taught otherwise.

I don't know if this kind of thing happens in Switzerland, but here in New York, there are many cases where people (usually 'macho' guys) who deliberately go out and adopt big powerful guarding type dogs (sheps/rotties/pitbulls) and then these guys actually encourage and intentionally reinforce aggressive behavior in their pet dog because they like it that their 'big bad dog is tougher and meaner" than the other guy's dog. It is like an ego thing and unfortunately, it teaches the dog that being aggressive and assertive is ok and acceptable to the owner. Rex will need to be taught by you another way of being when he is around other dogs.

This subject you have brought up is huge with lots of possible ways to start tackling this, and there are so many things that would need to be done to get Rex on the right track that I think that if you do some reading on this and get some tips, you can train Rex out of this behavior eventually.

Do you have access to books on dog training at a library near you? Are there dog training classes or professional obedience trainers near you that can help you?

Because Rex is a few years old, it is going take more effort to teach him "right" behavior than it is to teach an 8 week old pup. Is there a way you could hire a professional trainer to help you train Rex to change his ways? If there are trainers near you, that is the fastest way to get these issues you've raised corrected so that you will be able to take Rex anywhere because a trained and obedient dog is a joy to be around. A trainer is a great way to make this process the most fast, effective, and productive.

If there aren't any trainers near you, then I'll bet there are lots of articles on this type of thing on the web and in training books that you could get at the library. You could search "dog aggression" on the web and see if that helps. And books on correcting unwanted dog behavior will help because they give you specific tips to change what Rex is doing.

I understand your impulse to not take Rex places because what if he sees another dog and acts up? I think that if a trainer helped you with lessons to desensitize Rex to the presence of other dogs,that you would then be confident to take him places if he behaves politely. Unfortunately, if you don't train him to get him to that point (of being a polite member of society), it will be an awful nuisance going for walks or going to the veterinarian because any time he encounters another dog, he is going to go into this obnoxious barking and posturing behavior. A really good thing about Shepherds is they are so smart and their intelligence means that they are trainable and can learn things. So it isn't hopeless or anything.

Also, I think you'll need to be a definite Alpha to Rex in your household or else he might "take over". I think obedience training will help tremendously.

What does Rex know yet? How dominant is Rex with other people? Is he challenging you to be alpha in your own house? Does he know sit, down stay or any obedience commands? Does he jump on people when they come in the house? Does he listen when/if you give a command? I'm just trying to get an idea of what level he is at with respect to what he has knowlege of training wise.

Best regards,
Anna Lisa