well i keep my flat stomach from eating in a window, fasting, and eating a natural whole food organic diet.
as the guys said if your muscles are covered in fat you won't see them in the first place.
now as far as abs i work them out plenty so not sure why you think otherwise. i do pyro pilates which is 10X harder then weight training which works my core. i also do tons of weighted situps and also work my abs will pullup crunches too. the abs are a muscle group you can overtrain but again you need a flat stomach to actually see them, i am sub 7% body fat and sport an 8 pack year round. i don't believe in offseason's and all that bullshit. that is what i believe in but other guys have different goals so to each their own.