Your encounter was with a "rude" dog and an uneducated owner. There was a link to an excellent article on another thread. I forget which one, perhaps someone else can direct you to it.
Take heart, my dog is not a sissy with other dogs and he has reacted in much the same way with other charging dogs. Not that the dog who was charging up was probably a dominant dog, it was the way in which he approached your dog that probably offended him. My dog also has a strong sense of personal space with other canines, and he has been well socialized since he was 12 weeks old.
You don't have to let your dog play or interact with others, but he should learn that while on leash and walking he should be ignoring other dogs. Walking at a good pace and not stolling when you see another dog coming helps.
I had a similar incident a couple of weeks ago. I was walking my dog off lead with a friend to a rocky outcropping by the lake. All of a sudden my dog was behind me pinning something to the ground. It was screaming. I thought it was a squirrel. I nearly had a heart attack. It was a min pin. The owner came rushing up from about 30 yards away. I said "Max, off!" He released the dog no harm done and it hightailed itself back to it's owner who I heard say "Bad dog!" Now it could have been much worse and I would have felt awful. And that's why if you let your dog off lead it has to be 100% reliable.

I know what you mean oldearthdog. My dog was on a leash minding his own business. It was her dog that was off leash in a public park, and it was her dog that ran up to mine. And I did yell to her to call her dog and she just ignored me. Oh well, I hope she found her dog though.

I hope she found her dog though <img src="/ubbthreads/images/graemlins/laugh.gif" alt="" /> Kinda says it in a nutshell doesn't it!

Any thoughts about this:

My gsd is extremely tolerant of dogs when on a lead, when off lead in a neutral enviroment he tends to either ignore other dogs or, when confronted, will dominate other dogs generally by rolling them or mounting them but will immediately stop when told. Certain dogs however make him crazy. If he sees a newf he immediately wants to knock the snot out of it. same with pit bulls. He hasn't had any problems with either that would lead to this behaviour. he is also fixated with medium sized light colored dogs w/ short hair i.e. yellow labs, american bulldogs. he simply wants to chase these dogs and mount them constantly, but not aggressively. What is it that makes him act in a particular way with certain breeds of dogs, but not others? any thoughts?

Why they pick out certain breed for no "obvious" reasion, who knows? I knew a lady that raised Cocker Spaniels and her one stud dog, a blonde, would only breed with other blondes. Is that predudice or just a blonde thing <img src="/ubbthreads/images/graemlins/laugh.gif" alt="" /> , who knows why.

Do you think it could be more of a size and gender thing than a breed thing? I noticed with my last dog, who was a 110lb Shep/Lab X, that other smaller dogs would always want to start something with him. He would pretty much mind his own business most of the time, but these other dogs were always pestering him. It was pretty funny, one time when we were walking, this little Chihuahua came running out from its house at us, barking its little head off. It ran underneath my dog, and started attacking from below, nipping at his legs and belly. My dog just kinda looked at me like "Give me a break!". We just kept walking, and the Chihuahua finally went home. But this was pretty typical of how most smaller males would respond to mine. I think he just had a self confidence, coupled with his size, that triggered the response.

Now, I realize a GSD isn't a little dog, but I noticed that the breeds you mentioned are either larger than yours, or within a certain size range.

L. Swanston
Good thought on the size, color thing. Who knows what goes on in their heads. Talk about confidence, That Chi dog was "under" your dog. Confident or nuts mabey, but those little guys have a lot of brass.

My guy is way oversized, about 115 lbs and trim, and also ignores small dogs who challenge him. It's almost as if he finds it to be amusing. The dogs that really set him off are both male and female, older and younger. He's gone after two 1 yr old newfs who are quite a bit bigger, but also a 9 mo old puppy who was smaller. the pits were also samller - about 70 lbs. also, over the 4th holiday he met a viszla - about 55 lbs - and immediately tried to crush him. but, with certain dogs, generally smaller, he tolerates them jumping up, even snapping, and just looks at them like they're crazy. can't figure it out.

Who knows....it could be something as simple as looking at him the wrong way. Something that he would forgive in a little dog, as he doesn't feel threatened by them at all. The puppy may have been an issue of teaching him some manners, much like you would a rowdy teenager. It's tough to say, but I think it's just like with people, some folks just rub you the wrong way.

With the newf puppy the incident occurred in a dog park (I know, but with the leash laws and limited open space in Chicago sometimes it's the only option) with the puppy entering some 100' from my guy who immediately bolted after him. it wasn't a case of correcting a rude dog. Also, while I certainly understand that some dogs will rub him the wrong way, why would that carry over to certain breeds? or is it simply an association he makes - ran into one newf I didn't like so they must all be annoying? I'm more concerned with the pits, that could get ugly quickly and result in a visit to the emergency vet.