What do you mean by "mouthy?"
At 9 months a dog is no longer teething. Mouthy puppies, are generally exploring their world with their mouthes, and teething. That should be done with by 9 months.
It will not be done if the dog is rewarded in some way for doing this.
Depending on what "mouthing" is, I think maybe you should google NILIF. Privileges are what exactly? Extensive attention is what exactly?
You need to give positive attention for positive behavior. No petting unless there are four (paws) on the floor. When mouthing starts, remove that which is being mouthed and do not give attention for mouthing. None. Game Over. When a pup gets over exhuberant during play or what have you, and behavior is getting out of hand, game over.
Attention is something that should be initiated by you and given by you and ended on your terms not the dogs. You call the dog over and pet it, don't pet it when the dog nudges your hand and asks for it. Usually, a dog will be fine if you do these things, but when you have a dog that is pushy, or rude, or trying to assert itself in ways that are not acceptable, then, you have to consider all of these things, and change your management style.
Look into NILIF (Nothing in Life Is Free), it's a place to start.
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