Spend the money on at least a couple of in-home sessions with a trainer. An untrained German Shepherd with access to chickens, ducks, sheep, and goats? Let your imagination run wild!
The puppy is displaying territorial behavior already? That's early. Make that trainer a certified behaviorist. You may be misreading some other behavior. Either way, you don't want Cujo patrolling your farm when the mailman comes up the driveway. A behaviorist can help you read your dog and let you know if there are any issues you need to really work on.
I read everything I can get my hands on. Behavior. Theory. Training methods. Body language. Books, TV shows, Web sites, message boards, you name it. There can't be a method or theory I couldn't at least summarize by now, but all that knowledge has been worth zero to me without hands-on experience. I've made a lot of mistakes that could have been easily avoided if I'd spent a couple of hundred on in-home consultations from the beginning.
Get someone out there with you. You'll thank yourself later.