2 ways : - In 30 days with "view solution" - By doing some research (shouldn't be too hard)... I haven't seen every movie I find and i guess you haven't judging by your score!
This one is not a really big spoiler i know, but I would hate to be frequently spoiled by What the movie pictures When I'm uploading I always wonder if the picture will contain any spoilers.. And the death of a main character is a big NO NO for me WTM is here to make us watch movie, not the other way around (what if it was a key element about the ending of The Sixth Sense, Donnie Darko, Mulholland Drive, Memento, etc...)
guzo: You always have it in your own hand. If you've seen the movie, you can't be spoiled and if haven't seen the movie, 1. don't do research 2. don't press "view solution"
A spoiler (for me) implicates, that you have no chance to escape crucial information.
However, I agree with you, that posting the death of a main character could be a serious spoiler and should be avoided. And could you please tell me how to spoil memento? The film spoils itself in the first scene ;)