The wiring in your house doesn't suddenly get all lax and sloppy when you put in a smoke alarm. It doesn't know the difference.
A pre-nup or a secret divorce fund, however, means that one or both parties know they are not really committed to the marriage, and therefore are less likely to work at it if problems (or a 'better' offer) come along. The same way you will be much quicker to, say, quit a job if you know you've got something else to fall back on.
As for second marriages, especially of people who have lived alot of years and are widower/widows, I firmly believe in prenups to protect the children from the first marriages. I have seen horrible things happen to kids when mom or dad marries somebody late in life.
I for one believe in a prenup if there is a substantial difference between spouses, at least a time limited prenup. And I would sign one willingly. But when both are entering the marriage at the same level, broke as we were, why have one.
And having secret accounts is just plain dishonest. Except for my little stash of husbands quarters and nickels that I steal nightly when he plops it out on his dresser. That doesn't count. And I love stealing it and he knows I do it and thinks it is "cute"