Preheat your oven to 350 degrees.
Cream together the shortening & margarine. Beat in the light brown sugar along with the white sugar until smooth & creamy. Add in the eggs & vanilla extract; mix well. Stir in the flour, salt, & baking soda. Fold in 3 cups of old fashioned oats.
Roll the cookie batter into small balls, about 1 teaspoon's worth or so. Place on a cookie sheet that has been sprayed with non-stick cooking spray. Using 2 fingers, lightly press down on each cookie dough ball to slightly flatten it. Don't completely flatten them, just press down lightly so they're not a round ball anymore.
Bake for 8-10 minutes. I find my cookies are done in exactly 10 minutes, and not a second more. You don't want to overcook them! After baking for 10 minutes, remove from the oven and allow to cool on the baking sheet for a few minutes; then transfer the cookies onto a wire cooling rack to finish cooling. They will crisp up as they cool.