Diogenes blogs upon declining rates of Catholic marriage in the Archdiocese of Boston. One of his commenters complains that it is because not enough clergy are talking about mortal sin.
I think it goes deeper than that. People need to hear more about why the Church is right about marriage, and not just why the world is wrong. The priest who prepared my husband and me for our vocation as a married couple told us one day that Catholic marriage is what everyone wants deep down, but they don't know it. Having now reached the end of my first year as a married Catholic woman, I have to say I believe this is true. Unfortunately, many people with whom I talk about Catholic marriage, and even more people whom we see in popular culture, do not understand this, and write off what the Church, it's Scripture, and its Tradition say about how marriages should work as being outdated, impractical, impossible, or irrelevant.
Perhaps the best way to renew marriage in the Church is for married couples who see why Catholic marriage actually works to witness through their own families to those around them. This can be done in an official capacity, such as through Marriage Encounter and Engaged Encounter weekends. It can also simply be a question of living your life, and letting other people see it so they say, "I want a marriage like that!" My husband and I both know people, even in our own extended families who do not understand the fullness of what marriage can be. We hope, that as we live out our vocation, God will use us as an example of what is possible, even when the world says otherwise.