I'm a dividing line at an edge; a squiggle of land lacking rock or ledge. I stretch out far and sometimes wide, but you'll stay dry if you pick my side. There's salt on my breath, and I've sand for feet; you sometimes sit with me in the heat. When waves come to call, I hold them back- keeping your visit right on track. But remember, should they ever choose to rise, those who leave surly are wise. What am I?