bobad, if the oak is seasoned, it should be OK. Unseasoned oak has tanins which can be lethal. I killed a big batch of fish when I stuffed a whole bunch of freshly pushed green oaks into a pond for habitat.
BTW, it sounds like drilling 1" holes into 18 to 24 inch oak would be hard work. I can't imagine going any bigger.
I question the effectiveness. It seems to me that the holes would clog up with algae and other junk. Maybe not. A lot of people have used pallets, rocks and other stuff with good results. Fatheads are a fairly shallow water fish. I wouldn't sink stuff too deeply.
