I have some (8gal?) rubbermade tubs that fit three .50cal cans in them with room for more stuff on top. I label them "winter clothes" or "old kitchen stuff" and stick them down next to a bunch of other rubbermade tubs in my basement.
It's really obvious if you try to move one of the ammo boxes... they weigh 100+lbs each.
Since HoneyBadger Jr is getting more mobile (he's almost walking now) I need to come up with a new solution. I'd like to finish the basement soon, which will give me an opportunity to build in a secure closet to keep things out of his reach.