I do not want my boys growing up thinking that foul language is acceptable!
Do you have any advice?
Perhaps you could say something like, "I know that you don't want to set a bad example for our kids by using foul language in front of them so much. You're a good dad, and something must be really bothering you if you can't keep your anger and language in check in front of the kids. What's really going on here? What's bothering you?"
Has he always used foul language in front of your kids? If this is new behavior or if it has gotten worse, then my guess is that it's a response to something that's going on in his work life or family life. How are the two of you doing as a couple? Could this be a result of some problems the two of you are having?
Clearly, your attempts to reason with him are not getting a rational response. Perhaps he sees stopping the foul language as a loss of power. If he swears in front of your kids in the presence of a family member or friend that he respects, you might want to enlist them to mention their concern to him about his language.
Seeing a counselor could be a big help, but I would be surprised if he will agree to that idea right now. Let him know that you believe him to be a man who is better than the language he is using and that you'd like to know why his language doesn't match the good father and husband that he is. He is angry inside and he needs to reveal the reasons for his anger before he stops his foul language in your home.