Acts like Cujo when people come to the door
So here I am with yet another question (issue). Forest is so sweet and gentle, EXCEPT when someone comes to the door. He acts like Cujo! Barking and growling with hair raised and trying to jump on them. It's embarrassing and rather concerning. I truly believe this is all bluster because within about 30 seconds to a minute, He is fine with who ever it is, and becomes his usual sweet, goofy self.
I'm not sure what to do about this. I have tried putting him on the leash, and making him sit, and praising him and offering treats for sitting quietly. As soon as someone walks through the door my highly food motivated boy, could care less about those treats.
We will be attending obedience classes but those won't start until the end of August. He needs to understand that this is in NO way acceptable behavior.
Help!