Well, why chew up the things he loves when there's so much wood and bushes available? You could try bitter apple for plants, but it might be worth putting some chicken wire over the deck lattice and perhaps some repellant around the bushes. Have you tried obedience work? Labs are very intelligent and easily bored and that is most likely his problem. Also, since he is a retreiver, he's more "mouthy" than say a pekinese. Could he have a "woobie" to play with outside? You know, a piece of fleece or some such to toss around and chew on. It may also be a bit of separation anxiety and the obedience work might well help that. Let us know how it goes. Good Luck.