Sharon, you mention a very significant fact... "He's a great dog, but he is a young field lab. It is part of having such a breed. Love him to death."
Although each dog has its particular personality, pure bred breeds generally somewhat conform to a general set of behaviors. That is where not knowing or researching a breed can become problematic. If a person wants a certain general set of behaviors and selects a dog whose breed will probably not exhibit these behaviors, that selection can be a source of problems. Trying to train a dog to become what is not natural for the dog can make both dog and owner unhappy.
A perfect example is your selection of field Labs who have more energy and higher spirits than say, the more sedate English Labs. Trying to make a field Lab into a sedate low key dog would not only be difficult but, could be detrimental to the dog.
I selected a Great Pyrenees for several reasons... First is that they are protective of their area and the animals and people whom they are charged to guard. Second is that they are generally "safe" guardian dogs - in that they are not known to be biters (although it is said that a full grown Great Pyrenees has enough strength in its jaws to break the back of a coyote). We decided to get a guardian dog after a local small dog was killed by a coyote within a fenced yard. Coyotes have no problems scaling a six foot chain link fence. I figured that if a Great Pyrenees can protect a free range herd of sheep from coyotes, protecting our small rescue dogs within a fenced in property like my yard should be no problem for the Pyr...
I knew that generally, the Pyr doesn't take to standardized training in either AKC obedience or AKC Agility because it thinks for itself and doesn't follow commands blindly. IMO, the trick in training Serena is to use strategy to make her WANT to do what I want her to do. Any example of this is that although she is learning house training better than I expected, she is not totally reliable in house training (the Pyr is slow to mature). Thus she sleeps at night in a large crate with a soft bed and several of her toys. I keep the door open during the daytime and she is free to come and go, It is surprising how often we will find her sleeping in the crate during the day with the door open. When I want her to retire to her crate for the night, I have a large Kong toy into which I stuff some chicken jerky treats. I toss this into her crate and she follows it in for a good chew. Since she only gets the Kong at that time, Serena will run to her crate whenever she sees me with the Kong in my hand. Along those lines, shaking the treat bag will generally attract her from anywhere in my large yard.
Speaking about yards, I a fortunate in having sufficient property for a large dog like Serena.
Trying to keep a large dog with guardian instinct in an apartment (or even a very small yard) could be counter productive. Additionally, while in the process of house training, if I had to take her for a walk every time she needs to go out - that's all I would be doing. Also, I have enough property to provide an area for leash training.
I knew that Serena will grow very large but, although I dearly love our small dogs, I absolutely adore big dogs... I knew that a Pyr can be gentle with the animals like lambs it is charged to protect but, it makes me feel great to see her playing with one of our younger Maltese who has only three legs. Although the play can become quite animated, Serena is very gentle in her actions.
What I didn't realize about the Pyr is how her guard hairs will keep her from getting dirty... Although she can get dusty and dirty playing outdoors, the dust and mud soon flakes off from the guard hairs and never reaches the undercoat.
I was also pleasantly surprised at how much Serena enjoys playing with toys. She entertains herself for long periods of time tossing around a toy and playing fetch with herself.
All-in-all. rescuing Serena has been (so far) a win-win proposition for both Serena and her new human and dog family!