The existing answers have some good tips and ideas, all based on the premise that the swearing should cease. I agree that hearing your 12 year old swear is not pleasant, and support you for wanting to nip it. Also, I absolutely agree that washing out the mouth is too extreme. In my opinion it actually is abuse, even though it was used in the past. I think it is a very good plan for the parents to swear as little as possible within earshot of the kids. Kids learn best by watching you.They may not listen to what you say, but they WILL watch what you do!

But here is a little different idea. Besides cleaning up your own language, and letting your child know your swearing "policy," consider ignoring some of the swearing unless it is directed in a hurtful way toward you, another person or the child herself. Do set boundaries and consequences for swearing that is used as a fighting tool.  But if the swearing is tension relief and general expression of frustration, too much attention paid to it may offer too much "secondary gain" for the child. If that happens, the extra attention paid to your child, even though it is punitive, might just keep the swearing going.

So, if you feel open to it, try some planned ignoring and then keep an ear peeled for a time when your frustrated preteen says a different word or tries a different stress strategy.  Then use reward instead of punishment.
"Honey, I am so proud of the way you handled that frustration."  You did not curse, so I think -----------------(In that blank would be the reward you offer. You know your own child, so you will know what she would like.) You might give a little extra free time, computer time, TV time, or a special trip to the mall. Depending on your time, availability and finances, see how rewards work.    

And keep in mind, no one is perfect, the kids or the parents.  Some cuss words will slip out. If you expect perfection, you will set everyone up for failure and may be at risk to think your child is on the brink of "deliquency," and to put yourself in the role of a policeman. But do decide on some consequences for the gravest offenses. Keep consequences reasonably small, consistent, and be sure they don't torture the parents.

For the most part, I recommend staying pretty calm about most of this type of behavior because kids experiment. Do stay aware of your own stress reduction habits, and possibly teach some helpful stress relievers to your child. You can let some of the swearing go by when safety is met and the words are not designed to put anyone down. Think about whether the foul language is a bid for attention.  If it is, think of positive rewards for the behaviors you want. Overall, I would not be too worried because I have read nothing to indicate that swearing is a gateway to ruination.  Too much pressure however, can create conflict between parents and children that can make everyone miserable.

Bette J. Freedson, LICSW, LCSW, CGP

Tricky one! I actually don't agree with the idea that parents have to accept the fact that kids have a right to do EVERYTHING they see their parents do. There are plenty of things parents do that kids can't or shouldn't do (drive, vote, go to work every day, drink alcohol, etc). Part of the hard work of being a good parent is helping kids understand why they can't do those things now and how they can do them responsibly when they're older.

However, cursing is something I think is unattractive at any age so I think it's great that you and your husband are working to reduce your use of foul language. It gives you a chance to model manners and self control to your child which are great things for her to learn from you!

If you're using curse words as exclamations (when you stub your toe or make a mistake at work for example), it means cursing provides a kind of tension release for you. (You feel a little better after you say the word). Maybe you can find some "alternative" words that provide the same stress relief without feeling "hokey". I often say "sugar" instead of the more offensive word that starts with "Sh" and it actually feels pretty good!

You can also try some behavioral habits that will make it less necessary for you to curse in tense situations. Tell yourself you have to take 3 deep breaths or count to 5 slowly before you curse. If you do one of those things you'll almost never still feel like cursing after.

If you and/or your daughter are using curse words as adjectives spend some time looking up words to use instead. You can actually get a lot more powerful and descriptive using standard language than you can using curse words.

Once you find something that helps you stop cursing, you'll be in a better position to talk to your daughter about her behavior. You could say something like "Our family has gotten in a bad habit of using ugly words when we're angry, frustrated, or injured. I don't think that's the best way for us to present ourselves to the world. I know lots of people express themselves in this way but I think we're better and more creative than that. From now on your dad and I are going to stop cursing and it is our expectation that you will too. Here's what we're doing instead [insert your plan here]."

You should set up a consequence for cursing that EVERYONE has to live with. You could set up a reward that everyone gets if they don't curse for a day or week or you could set up a negative consequence to be given every time you do curse (a dollar jar for example).

Once you break the habit, I bet you'll find that you feel happier living in a house that communicates without cursing.

Good luck!

Kat