you also have to consider that some dogs will never outgrow the chewing stage although it does obviously become less prevalent as the dog gets older.
My first guide dog was a yellow lab and she would chew whatever she could lay her paws on if left alone. In the first six months I had her this included:
A cushion
four meters of wrapping paper.
A set of modem cables that belonged to dh' work (ooops).
A sweatshirt (well she just chewed off the arm .
And this was an eighteen month old dog that had been well-trained as a guide dog, was exceptionally obedient and who did come to work with me every day obv and slept in a basket under my desk and we went out at lunchtimes. But she didn't like to be on her own as she was so used to being with people and so when left she went looking for things to do.
Just three months ago I came home and found she'd chewed up a letter that had come through the door, and she was nearly fifteen then. (we had to have her pts in December due to a tumour )
What you have to bear in mind is that these are animals. And even if you put in all the hard work and the training etc they are still animals with their own personalities and querks.
I now have two lab x golden retrievers (one is a soon-to-be retired guide dog who is being retired early due to a behavioral issue, and the other is a still-in-training guide dog who I am being trained with atm). The older one is fabulously obedient, perfectly sociable, loves people and children, I can take him into school and meetings and the classroom and he will lie at my feet and not move even with 30 children shouting and running and causing a noise. He is an excellent guide dog and works incredibly well.
When not working he is brilliantly behaved in the house, has never chewed anything, although he's an opportunist with food and did eat a box of chocolates that landed him at the vet, but other than that... His recall is perfect, he doesn't run off.
On the face of it he is a perfectly trained, well behaved dog. but...
He doesn't like other dogs when he's on lead/in harness. He reacts very strongly towards them in fact - barks at them and will growl at them, although is perfectly happy to make friends once I have done so, and he only reacts like this when restrained.
We have tried everything to break the habbit but it is simply not possible. Trust me I have tried everything - vets and behaviorists, and special collars and reinforcement training (praise the good behavior, ignore the bad), but the behavior is so ingrained in his psychy that he cannot be trained out of it.
And so because of this (and predominantly because a member of the public complained), he is being withdrawn as a guide dog next week.
But looking at him you would never know.
The querks of the new dog have yet to emerge
I guess what I'm trying to say is that even if you have the time and the patience and the inclination to put in the training, a dog is an animal, and it will always have querks that are a part of its personality.
You can buy a puppy and hopefully train it to fit in with your family, but you also have to be prepared to fit in around the dog to an extent (much like having a baby).
Are you prepared for that?