When using the content network, you can specify sites you don't want your ads to show on. Click on Exclusions when in the Networks section.
Much thanks LucidWebMarketing, Is that the drop down menu titled: Add_Exclusions/Exclusive_Placement ?
Yes, it is and you just put the domain that you dont' want your ads to show in it. Many site is MFA and they are not a good site to advertise.