What are the options available to us so we can be sure to have a child without cystic fibrosis?

Screening. If two parents are both potential carriers, screening will reveal your risk. The only way for two carriers to avoid having a child is an elective abortion after an amniocentesis and genetic screening of the fetus. Children with cf, however, are children that can live full lives, and there are promising treatments on the horizon.
Cystic fibrosis. Prior to pregnancy, or early in pregnancy, you can have a blood test which shows whether you carry a cystic fibrosis mutation. Both you and your spouse must carry a mutation to be at risk of having a baby with cystic fibrosis.