The Lake Hermitage project is, by most measures, a model of restoration. One of the early efforts proposed to help Louisiana recover from the 2010 Gulf of Mexico oil spill, the plan piggybacks on existing construction, adding 100 acres of marsh east of a shallow lake nestled between the Mississippi River and Barataria Bay. Not far from some of the spill's most oiled shorelines, these brackish pockets of open water will once again support the sway of cordgrass and, it is hoped, the cranky call of blue herons. Yet despite all this planning, one fact remains: If everything goes right, the marsh will last only two decades, matching the ecological services provided in five years by a natural wetland. Then it, too, will start succumbing to erosion, subsidence and rising tides. The Lake Hermitage marsh will be born with an expiration date.