Is there a way to convince my lab that it's not ok to hold my hand in his mouth? I know he's not biting, and that's just something labs do, but I'm pretty other people wouldn't feel the same if did the same to them.
Could you not use the same technique as stopping them biting, by yelling/"ouching" when he does it, so that he thinks he is hurting you!!
Replace your hand with a toy every time. Soon they will greet you with a toy in their mouth. They are retreivers and are mouthy by nature. Correct it everytime with a no bite and give them an appropriate toy
I would say "ouch" take my hand out & replace it with a chew toy. It took patience but they finally got the message. Good luck.