You could also add clauses for money being added to the wallet, like on the consummation of the marriage, the birth of a child, wedding anniversary, as a % of any income increase the family has (since she indirectly helped generate that increase), etc.
Not the least because German law says that if something is given to a spouses, explicitly as a present, the recipient owns it outright and it doesn't become joint property. (That's why I receive gold coins for Christmas, birthdays, etc., where they are given in front of other people and come in a present box.)

You would probably have to tie the amounts according to some deflation rate, tho. The price of housing or electricity, or something.