The color is exquisite. The nail art is sublime. You step out the door of the salon, reach for your keys and — whoops, there goes your perfect manicure. A good salon manicure (the traditional polish kind, not the gel kind) can last as long as a week, but you can wreck it in just a few seconds if you aren’t careful. Professional nail artists have seen it all, and they’ve got some smart tips for keeping nails in tip-top shape. Once the manicure is done, you’ll be tempted to dash out and get on