The damage is typical of wind and cold damage which is indicated when the edges of the leaves become distorted and turn brown. This occurs frequently in plants that may be in a colder climate than recommended or in a location with severe exposure. Provide protection from winter winds and winter sun. Note, boron poisoning or fertilizer burn will create the same symptoms except uniformly over the plant rather than just on areas exposed to the sun and wind. Here is what it looks like (courtesy of Harold Greer):
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Putting the potted plant under a deck can keep it too dry and cause drought damage. Also you must shade potted plants from direct sun on the pot. Rhododendrons do not like warm roots. It is best to put the black pot in a wooden planter so the sun won't hit the black pot directly. Make sure the pot and the planter both have excellent drainage.