Appropriate age group(s):
Middle School
High School & Beyond

Description of technique:
One way teens seek to express themselves is by adorning their bodies, and if you've already told them that body piercing is out, the next option (in their heads) might be a tattoo. And they will probably do so regardless of your own parental philosophies on the subject.
You can certainly try to enforce the old adage, "not under my roof and not until you're 18.ö But a better tactic might be to help them educate themselves and to talk about the permanence of the act, the risks and the responsible choice.
Explain to them that both body piercing and tattooing carry high risks of transmitting Hepatitis, HIV and other diseases if performed under non-sterile conditions. Most tattooing establishments and artists are not regulated, licensed or inspected. That means that they don't have to require parental permission for patrons under 18 or enforce any health and safety standards.
Another idea is to have your teen talk with someone who got his or her tattoo as a teen. Have them discuss the pros and cons and any possible regrets. Sometimes insight from a non-parent (whose opinion you trust) can be very effective and much heeded advice.