Know-How Exchange : E-Marketing

If one is using an ad serving firm, like Google AdWords, AdRoll, etc., how can you keep your ads off of undesirable sites? I don't recall settings which would allow you to specifically keep off of these sites.

I am based in San Francisco, and my tech clients would all probably kill me if one of their ads showed upon a right wing place like Brietbart, Red State, etc. Wouldn't want the ads on the left wing questionable/fake news sites either (Occupy Democrats, etc.).

Looking for actual descriptions of what menus to go to, what settings to change, etc.

I do watch some key sites from time time time, and interestingly found a MarketingProfs ad show up on Breitbart - [link deleted by moderator]. Thankfully haven't found any of my clients' ads.