CAMP PENDLETON, Calif. (AP) -- The U.S. Marine Corps, known for turning out some of the military's toughest warriors, is studying how to make its troops even tougher through meditative practices, yoga-type stretching and exercises based on mindfulness. Marine Corps officials say they will build a curriculum that would integrate mindfulness-based techniques into their training if they see positive results from a pilot project. Mindfulness is a Buddhist-inspired concept that emphasizes active attention on the moment to keep the mind in the present.