Another trick to try--we noticed recently when we started adding yogurt and pumpkin to kibble, it made the kibble really sticky. Slowed them all down during meal times. Don't know if it would work with a labby, though--they
do seem to be rather exuberrant at mealtimes!
But it might be worth a shot. We used about 2 Tbsp of yogurt (a natural probiotic) and a tsp of pumpkin (a natural source of fiber)...the biggest of our dogs is about 60 pounds.