In general, there are a number of different  options for flat warts on the legs.  Best, but most expensive, is laser hair removal and, with the right type of laser, all skin types can be treated safely.  Next, would be the epilators or professional waxing (avoids the mess) with waxing being the most expensive of those two.  Your dermatologist is right that it's best to avoid shaving because it can spread the virus that causes the warts.  Better than the Retin A though is prescription Aldara cream.  A dermatologist or your family practice doc could prescribe that for you.  Hope this info is useful!