I would like to train my dog in one of the protection dog sports. I also want a nice family dog. Will this training change my dog and turn him into a liability?

Question from Miguel: I'm interested in either protection sport training or Schutzhund. My concern with doing so is that I still want my dog to be friendly and a family pet, as I have two children. I'm wondering if awakening the aggressiveness through training would change his good temperament. Any advice and/or suggestions would be greatly appreciated.