coldcazzie
Ice Queen
It is true that most of the time that it is due to the owners rather than the dogs for them being aggressive. There is no denying that some traits are set into dogs genes more than others though. GSDs for example, since they were mentioned earlier, were bred as guard dogs in Germany, so are incredibly loyal to their owners. The majority if socialised correctly are fine with other dogs and people, however they will always have the "gene" if you like for wanting to be very protective of "their" land and "their" owners, if they are not corrected as a youngster. This said, it is not impossible to teach an old dog new tricks. I myself have trained dogs who were extremely aggressive towards other dogs for no apparent reason. Within a couple of months of training, patience and discipline, they have been playing with other dogs running about in a field together, unmuzzled without aggression. I'm a great believer in the idea of being a pack leader and feel that more (generally) strong willed dogs such at pitbulls and GSDs will more easily assume the role of "top dog" and try to rule the roost, however I feel that any dog has potential to be friendly and non-aggressive with proper, assertive leadership. It's just a shame that it is lacking in many of todays dog owners.
I knew it would only be a matter of time before someone said something that sounded like Cesar Milan!