I have come up with 3 uses in ponds for cement mixing tubs. Floating land area,
hide box, nesting area.
For the floating land area, I attach empty water bottles on the inside of the tubs using zip ties (drilling holes in the bottom of the tubs), then I attached indoor-outdoor carpeting to the top, so the turtles have something to climb up on, also attached with zip ties. Then I added some scrap pieces across the opening at the bottom, so turtles can swim up underneath and hide in there.
For using it as a hide box, I cut a big hole in the side, then attached rocks to the bottom with zip ties, then sank it upside down in the pond. This gives them somewhere to hide in the bottom.
In the land area of my ponds I have mulch, but have 1 or 2 mixing tubs sunk into the mulch with a mix of sand and peat moss. Usually turtles will rather lay in these boxes than the mulch, making the area to search for eggs smaller.