Only thing that worked for our lab was exercise. Days we took her out for a jog twice a day she didn't chew near as much. We tried everything we could such as bitter spray and Tabasco and she acted grateful to us for giving her extra flavor to chew on. Then we started a pretty strict exercise regimen and she did much better. Of course they still chew, so there is no 100% cure...
I agree with exercise although my issue was/is with digging small holes. My lab puppy just turned a year old and if I walk her about 25min in the evenings then she will not dig but if I don't walk her she is a threat to dig a small hole somewhere in the yard. Lately with the rainy days/evenings I have skipped a few walks and currently have two softball sized holes dug in my yard. More/extra exercise doesn't seem to have a carry over effect. I hunted her Friday and stayed the farm Fri, Sat and Sun with her constantly playing with other dogs and running quite a bit alongside the ranger but come Monday I didn't walk her because I was busy and she created one of those holes Monday evening.