Locking mouth shut with certain things...mostly socks!

[Catherine & Dexter]

We have a 7 month old goldendoodle - Dexter. Sweet and affectionate, has done really well with his training so far. Good with our 3 young kids. The problem is a couple of times now he has gotten hold of things that he really loves - socks, a braided bracelet of my daughters. In these times, he has not allowed us to open his mouth and remove (as he normally would). He locks his mouth closed and won't budge. He actually pulls his paws up towards his mouth too. He goes Into total lockdown mode. Will.not.budge. Gets stiff and stubborn
I think we need the drop it command - he really doesn't know this one yet.

We've tried:
Trading a high value treat for the sock. Nothing - he doesn't even budge.
'Give it, take it' - nope, not interested in that either.
I have had to just wait and loosen it up and it has taken us 20 minutes at times to get it out of his mouth.

This has happened 3-5 times in the last couple weeks.
He is not neutered yet, we are trying to wait until he is 1 year old. No other aggressive behaviors present.
Any suggestions? He is so sweet and such a great dog
Tell me this is a phase!?!?

[Stella]

My guys used to love to steal socks when they were younger and parade around the house with them!! Hartley would toss the sock on the air and catch it again!! They do eventually grow out of it!

[Christy&Riley]

Riley is super sweet but man can she be stubborn if she gets into something she isn't supposed to have. Swapping for something else didn't work. She would just eat what she had and then sit pretty to get the swap item. Kind of defeats the purpose... :-/ I'm too scared to force open her mouth so that is likely why she obeys my husband more in these situations. I also learned that getting angry made her clench harder so I changed my approach. She has been doing much better if I calmly tell her to drop it in a low authoritative voice. She has actually started dropping wood chips when I tell her to. That's huge for us!

the only way that worked to teach her drop it was as a game.I threw one toy and when she brings it back I say drop it. She has to drop it before I throw the second toy. She loves chasing toys so she would almost spit the toy at me so I would throw the next one. Now she drops it early to get a head start on the next toss. I make her come back and bring it closer. She pouts like a teenager. LOL