Ok, I have a semi-portable wood rack made out of cinder blocks, lawn timbers, and 2x4's. Should hold about 1/2 cord. I've had it collapse twice now in the last week. Normally I stack against a wall, so haven't run into this issue. It's the wood itself that is falling, the rack itself stays upright. I think at least part of the issue is that my splits are short (14-15"). So I need some sort of bracing I guess at the top. When I make my built in racks as part of my new fence, I'm going to put some lattice on the back side. I might do this, and then just put a 2x4 across the front. Wondering if anybody else had a more creative solution.