I own two Labradors now and have had labradors for 14 years. All are/were trained to the invisible (shock) fence, with little effort on our part I must say. They are eager to please and respond to reward more than punishment.
Labs must be exercised to the point of near exhaustion ( we use a tennis racket and hit ball after ball after ball,) we watch their individual signs that they are nearing the point of falling over.... our black one drops her ball a few feet away from the launching point or takes a quick run across the pool steps to grab a drink and cool her tummy. Chocolate girl's tongue goes out sideways. ANYhoo, my point is they will not chew, run away or otherwise be destructive IF they are well exercised and TOO TIRED! Just like Cesar says!
P. S. 'point of exhaustion' is just a term to describe the level of activity it requires to get these dogs tired. One or two tosses of ball just doesn't do it.