[steveklabnik]

I've heard that people have done this with twitter accounts; make a new account that's private, tweet random stuff. Once one of them comes true, say, "bart simpson becomes president in 2020", delete all your other tweets, rename the account to something like "bartsimpson2020", and then publicize the account.

You now have a timestamped thing from before it happens that verifies you made the claim long ago, but you've destroyed the evidence that it was effectively random.