Destroy all the rival pony carts in 'At the Races'.

During mission three, 'At the Races' you must destroy all pony carts before the pop up message appears saying "You Won." A fully upgraded disintegrator or thumpgun is the recommended weapon for this level. A machine gun will only work on the regular carts, so it is best to use the disintegrator for both the regular and furry carts. Also make sure to be taking out the gimp/furry pulling the carts, there is no need to worry about the one sitting in the cart.

Here is a video demonstration of how to do the achievement