Stains can be chemically bonded to the material and cannot be removed without damaging the material itself. Important thing is to avoid stains setting on the fabric which you want to remove. Avoid heat like ironing on it or pressing or folding or exposing it to the sun. This requires special chemical treatment and process to be followed. Proper brushing skills are also required. If you keep it dipped in the detergent can also help some time depending upon what kind of stain it is.