Drop It
If your puppy is not dropping the toy, you can't get mad at him. The puppy does not know that he is supposed to drop the toy. He needs to be taught this. If you just yank it out of the puppy's mouth, then he will not learn what he is supposed to do. He will only learn that the human will sometimes exert force and just take his prized toy away.
It is important for the puppy to learn that just because he does let it go that the play session is not over. You want him to learn that by playing by your rules that the game will most likely continue... Pam's Dog Academy
This video takes a look at an alternative way of teaching a "drop" compared to the usual swapping based techniques. I take a more classical conditioning approach and have found it works really well.
I would suggest that you do not use this with dogs who are "protective" over their food or other resources but work with a qualified behaviourist / trainer who may use a similar exercise if they see it to be beneficial and/or appropriate in your particular case.
Frenchie Revo who has resource guarding issues plays a daily game of fetch it and drop it as part of his training. In the video he has a medium value toy which he will 'drop' for high value home cooked liver treats. He gets an additional reward in that the game of fetch (which he loves) resumes - gradually food is faded out and this 'life reward' replaces it.