I just put them out for spring and summer fishing. As long as the old stumps along the river channel stay underwater they will last a long time. If I happen over there to fish with the water at winter pool I fish stumps and visible laydowns.

If you put out piles in what will be 15-20 foot in summer you can usually fish them with the lake on the rise in spring when they will be 6-8 foot deep or so. Then you fish for them suspended over the piles in the summer.

If I recall thermocline is usually 15-18 foot deep.