Cover a baking sheet with aluminum foil; spray lightly with non-stick vegetable spray. Break crackers and arrange on baking sheet; set aside. Melt butter, margarine, sugar and salt together in a saucepan over low heat. Bring to a boil and boil for 2 minutes; pour over crackers. Sprinkle pecans over top; bake at 350 degrees for 10 to 12 minutes. Let cool; break apart.