If you bury it you might be able to stop oxygen from getting in and turning into CO2, at least with any speed. But if water gets in you can still have methanogen bacteria come in and turn the wood into methane. Which you might be able to capture and sell and displace methane mined out of the ground but that isn't the same as locking it away forever.

This process is why you have methane production in swamps and conventional landfills.