I heard someone famous one time suggest that marriages should have a time limit, much as you suggest, and that like a business or job contract, when it expires, if both parties wish to renew it, they can choose to. But that should things no longer be working for both people, they should be able to choose to NOT renew it without too much hassle or heartache.
It would be nice if things worked that way...

"Marriage is a wonderful institution...but who wants to live in an institution?" -- Groucho Marx