Driftwood in dirted tank - Bury or not?
I have a 12-gallon tall tank (Marineland) which I'm planning on converting from gravel substate to dirted Walstad-style. I currently have a large chunk of driftwood which is low and flat, with great "caves" for shrimp, covering over 50% of the tank bottom. My question is, with a piece this large, should I put this on the bare-bottom of the tank, then fill the soil and cap around it, probably burying the edges, or should I set this on top of my substrate? My concern with the latter is large portions of the substrate that plant roots will never get to, and possible anerobic activity. Opinions? Anecdotes?