I like the bookends idea but I just lace my corners by alternating the direction the wood is stacked. No hardware necessary. The stack in this picture has been there for three years stacked on pallets on somewhat uneven ground.
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I used to do that when moving my usual 3 cord into the back porch. got tired of the time it took and sorting to get the right sized pieces when I came up with the 'bookend' idea. One of the few "smart ideas" of mine that actually worked.