Does burying wood actually work? I'm assuming it's a little more complicated than literally burying it, cause wouldn't it decay and release carbon at some point anyway?
Without oxygen, any decay is going to be incredibly slow. They're still pulling usable timber from trees that sank in rivers after being cut in the southeastern US 200 years ago. It's not cheap, but if you want some real old-growth oak, it's a viable source. And that's not a completely anaerobic environment.
As most of the heavy construction and earth moving equipment you'd use to bury the wood will be burning diesel and releasing carbon the entire time, you enter some new Tyranny of the Rocket/Wagon equation.