I run a combination of "White dogs" and Sarplaninacs. One of my White dogs is a full Great Pyr. The others have most likely been a cross between the Pyr, and who knows what other white LGD breeds. I started with the crosses who were already full grown working dogs. Really, I think I got pretty lucky. There was a local goat farmer that was selling his herd and 20+ dogs. I was able to take home some of his best dogs. These dogs were already working, were not being sold because of behavioral problems, and were able to teach me a lot about what to expect from a good guardian.
You can start with either a a pup or a full grown dog. There are pros and cons to either approach, but I encourage anyone who has the opportunity to start with a well trained working dog to do so. Not only will the dog show you how it should work, but it will also train future pups. This is hard to find if you want your LGD to protect birds. I've noticed that a grown dog not previously bonded to birds may have a tendency to snack on the birds.
If you start with pups just remember to give them enough time to grow and mature before they are put into a high threat enviroment. Yes, they should be with the animals they will eventually protect, but steps should be taken to minimize the threat from predators for at least their first year to 18 months. (I.e: pen the livestock indoors or near your house at night). A pup will attempt to protect it's charges from a young age, but if it's put in a situation where it's not physically strong enough to defeat the predators, it's confidence could be shattered.
With 120 acres, you will need at least 2 dogs. If you are in a cougar threat area, I would recommend a minimum of 3 dogs. Personally, I would run 4-5, but that is a lot to start out with. The number 3 for a cougar threat area is based on the way a cougar hunts. For the most part, a cougar will avoid LGDs, however, a motivated cat will hang out and wait until an agitated dog approaches. The cat will then attack the separated dog. A cougar is a formidable adversary that will inflict serious wounds very quickly. The severity of its attack will send most nearby dogs scattering, and this is what the cougar counts on. LGDs are a different dog, they live to give their lives in the defense of their charges and each other. When the cougar attacks the first dog, the other dogs will jump in.
I have seen the results of this first hand. My Pyr tangled with a cougar before I got her (actually she was given to me a month after the attack). During the attack, the cougar nearly skinned her alive. A month later her wounds were healing (she was given no vet care from her previous owner
), but she still had gapping tears over 5 inches deep, and both her canine teeth had been broken off. Had it not been for the other dogs who sustained no major wounds, I don't think this girl would have survived. As it was, she pulled through, no goats were injured, and the cougar that had been actively killing goats, and dogs in the area disappeared (I like to think it crawled away and died).
Breed is always a big question. All of my dogs have long coats. They prefer the winter, but even at 100+ degrees they adjust and do just fine. They enjoy a quick dip in the water trough, and spend most of the day in the shade, but actually seem to do better overall than my short coated house dogs. I recommend doing your research. Different breeds have different guarding styles and different strengths. The dogs that originate from western European countries tend to be a little "softer". I really favor the Pyr as a first LGD for this reason. They are very peaceful dogs by nature that resort to violence as a last resort. The dogs that originate in the east (Turkey, Russia, Armenia, etc...) tend to be a little more forward in their guarding. These dogs can be a challenge for a first time LGD owner, and if you choose one of these breeds you really need to do your homework to understand how these dogs protect and defend. Also, you will want to find a good breeder who has bred the dogs to maintain breed standards (guardian instinct and style), and will be willing to keep in touch with you to provide advise and guidance on raising the pup.