With a single command, you can add a NURBS sphere (a buoy) to your ocean and make it bob up and down in the water. The motion is restricted to the Y direction.
The Create Dynamic Buoy window appears.
By default, locators are connected directly to the expression, enabling you to rename locators without breaking the expression.
If you want to move the position of the locator interactively, the locator cannot be connected directly to the expression. In this case, turn on Free Transform.