One of the wiser things to do, when you're already married, is to align yourself with other married couples, preferably those that share similar values. If you have a peer group you go way back with, the better, because they probably know you and your partner well and they're more likely to also protect your marriage.
The Love Institute offers barkada packages for people like you. They offer a barkada package on parenting but am sure they can also easily accommodate groups to discuss things like affair-proofing marriages and marriage-spraklers.
This is also a great gift to your kids. Get other parents to shoulder the fees and get your child (and his/her peer group) to sit through a lecture on sex and dating, drugs, smoking and alcohol. At least they wouldn't be hearing about the horrors from you (and thus wouldn't be defensive) but you can discuss what they've learned and how they feel about what was discussed after.