You obviously cannot follow them everywhere, monitoring their every move. You have better alternatives for keeping them safe and teaching them to make choices in their own best interest.
Research tells us that kids who have good communication with their parents have a better chance of avoiding substance abuse. Families with good communication talk honestly and openly about their feelings and about such problems as peer pressure, teen pregnancy and drugs. Teens who do not use or abuse drugs usually feel that their parents love them and trust them. They have had a say in family rules and have been allowed to make choices appropriate to their ages and abilities.
If you constantly nag or make unfounded accusations, your child may feel that you neither love nor trust him.
Teens need to hear you say that you worry because you love them, not because you don’t trust them. Expect the best, not the worst.
Parents should make an effort to obtain clear, factual information about drugs and alcohol. Written information is widely available through schools, churches, libraries and the PTA. Read articles or pamphlets together and discuss them as a family, if possible. Share your concerns and values, but let your teen know that you believe he or she can make responsible, healthy choices in their own best interest.