I am going to drive a bunch of stakes into the bottom of the lake in 15 - 20 feet of water.

How tall / far off the bottom should the stakes stick? I've got a bunch of stakes that are about 4 1/2 to 5 feet tall. If I drive them 2 or 3 feet into the bottom they will stick up about 2 1/2 to 3 feet. Is that tall / far enough or do I need to get longer stakes.

Is longer better?