I know it’s been a while since you posted this but maybe this could help you or someone else with the same issue. I find the SRR method to work for many unwanted behaviors. This means STARTLE, REDIRECT, REWARD.
Dog mouth hand
You make a LOUD noise (can of pennies, hand clap, big voiced “HEY!”)
They stop, and look at you
Tell them to sit
Give a cookie
They forgot the bad behavior and you just reinforced a good behaviour. Eventually the bad behavior goes away, called the Extinction principle in the animal behavior world, and the good behaviour you have been rewarding prevails!
Good luck and I hope this helps!