Is he pretty good about staying with the animals? How close are your neighbors? How does your dog act towards strangers/mail man?
Some dogs perceive it differently. We had a medium sized dog that kept digging under the fence and playing in the street so we tried an invisible fence. It did nothing, she would go beyond the line, collar would begin to shock, could see her neck twitching, not a bit of reaction out of her. Our room mate gave the ok to try it on his pit bull, she did a back flip when she reached the boundary.
A great Pyrenees will grow to be a very large dog. If it is a smart dog that won't leave its flock to chase a threat a long way off, and you have no close neighbors, might work. It kind of depends on how its pain tolerance compares to its prey drive. Also unless your worried about people harming your chickens and goats, socialize this dog with as many strangers as you can from a young age. You don't want him attacking the mail man or random other person that shows up to say hello. He
should be aloof to strangers unless they are trying to attack your animals and you need to be able to trust that this will be the case if your not going to have a fence.
