Tons of info on his site, that's where I went when I found myself with a Dominant Aggressive male GSD 7 month old and had no "issues" for 18 months and then the crap flew with him and my Dominant Bull/Mastiff mix! Pack leader stuff he respected me but not one of the other pack members,,,"I" screwed up!!
I found a long list of mistakes that I had made with my first GSD (on his site). Starting with..here's the food, here's the water, bed rooms back there couch over here, there's the remote..make yourself comfortable!
If you only have the one dog you have more leeway, if you get a second definitely get his DVD's.
I have a couple of them- the Power of Training with Markers and Relationship Games. I really like them and you can catch them on sale pretty often. Go to the classified site on this forum and see if anyone has some for sale