You can get something called "underarm shields" at most chemists; they clip onto your clothes at the sleeve (on the inside of the clothing), and prevent any stains or dampness showing through. (They can't be seen through the clothes). They are washable and resuable.
You get rid of oil stains by using oxce clean
scrub it
Soda!
bleach is the most effective way to get rid of stains it removes all the dirt and cleares out the stain.
BK Comedy Series - 2013 Pit Stains 3-3 was released on: USA: 5 July 2013
When it's 99 degrees outside and the pit stains are profound.
your mom
peroxyed
You can either soak your stained clothing in the bleaching agents or detergents to get rid of the stains.
deodorant.
Rub it clean with arsenic
Try a little bit of Golden Syrup (see 'How do you remove grass stains?)