HELP! Need smart and strong dog proof container.

I need product recommendations.

My dog (German Shepard-Labrador mix) and both smart and strong, and he loves cat food. We keep dog food in his bowl at all times to try to avoid this, but he’s much more interested in the cat’s food. We keep the cat food in a 5 gallon bucket with a twist lid. He figured out the lid. So we put a baby proof thing on the cabinet we keep the bucket in, he figured out how to over power that. So I put a security chain on the cabinet door, the kind you find on apartment doors or on hotel doors. He figured out how to remove the cabinet door from the hinges and swing it open the other way. So now I’m trying to find a metal lock bucket big enough to hold a 20lbs bag of cat food. What I have seen so far doesn’t give me much confidence that he can’t get into to it. I’m here looking for product recommendations that will keep him out of the cat food so he will give up and eat his own food.