Aww, I made a cave with a piece of coconut shell I accidentally dropped in the tank randomly. I didn't like it's placement but left it for a few weeks found the ram had set up home in it and when I came to remove it I broke his/her little heart . Poor lil #28###.
Anyway, if its a tall piece of wood (tank height) I jam it down with something between the lid and it will soak. If its a short wide piece I just bury a large portion under the substrate to weigh it down. Of course this is after soaking it for a minimum of a week in a bucket. However a lot of buckets haven't got room for the wood I have which is annoying.