You can parent one layer to the other OR Alt-click on the 'stopwatch' of one layer's Rotation property. Use the pickwhip to drag/select the rotation property of the other layer. The two will always be the same then.
To bring up the Rotation property, hit 'R' with the layer selected. The pickwhip is a swirl icon that you click and hold, then drag over the property you want to link, then let go.