Here is the link for the video of the presentation made at Heritage by the authors of What is Marriage? A Defense: One Man, One Woman -- Prof. Robby George, Ryan Anderson and Sherif Girgis:

http://www.heritage.org/events/2013/01/what-is-marriage

They make the case for marriage in about 30 minutes and then offer 25 minutes of Q&A.

This is must-watch for those want to become better at articulating the positive case for marriage!