In a mixing bowl, cream margarine, 1 cup sugar, and brown sugar. Add eggs and vanilla; mix well. Combine flour, cocoa and baking soda; add to the creamed mixture and beat just until combined. Stir in 2 cup pecans. Shape dough by teaspoonfuls around each candy. In a small bowl, combine remaining pecans and sugar; dip each cookie halfway. Place with nut side up on ungreased baking sheets. Bake at 375 degrees for 7 to 10 minutes or until top is slightly cracked. Cool for 3 minutes; remove to wire racks to cool completely.