iirc, the way to mess with a sniper is to bound from cover to cover in less time than it takes to yell "Contact front!", [i]and[/i] to take turns.
-moving while behind cover to pop-out someplace hard to predict is good, too.

The other part is to make them second-guess whether or not it's you he's aimed at, rather than a twerky-twig.

Or you can wait until dark.