Dunes have to be sand dunes. Are there other kinds of dunes? Sand dunes are naturally kind of slippery because the sand slips as one walks up anyway; putting ooze on one is kind of painting the lily.
Therefore, to be possess’d with double pomp,
To guard a title that was rich before,
To gild refined gold, to paint the lily,
To throw a perfume on the violet,
To smooth the ice, or add another hue
Unto the rainbow, or with taper-light
To seek the beauteous eye of heaven to garnish
Is wasteful and ridiculous excess.
— William Shakespeare, King John, IV.II.10-17