RE: Puppy is busting birds...
There are alot of different schools of thought on this subject but I have found that starting a dog out on the right track from an early age is the best way to go. Mite's advice was right on with the check cord and is exactly what I would do.
The hard mouth issue is easy to fix with a good stiff bristled scrub brush...wrap it with a wing on the handle side and throw it out for him the bristles on the brush will teach him to hold it gingerly so he won't hurt his gums. I start all my retrievers out with this method and have found that it works wonders for hard mouths. It's also a hell of alot safer than useing nails or cigarette's.