Cream margarine and sugar. Beat in egg, lemon juice and vanilla. In a separate bowl, combine flour, salt and baking soda. Gradually add to creamed mixture until all is well combined. Beat in coconut. Shape dough into two 6" logs (or four 3" logs), roll them in coloured sugar or sprinkles and wrap in plastic wrap. Store in freezer until ready to slice (they're easier to slice when nearly frozen).
To bake: Move oven rack to upper position and preheat oven to 375F. Using a sharp knife, cut into 1/4" slices and place 1" apart on an ungreased cookie sheet. Bake for 10-12 minutes until tops are very lightly coloured. Cool for a couple minutes on the pan, then remove to wire rack to cool completely.