Or just plan a topic and a survey period. Eg if we're going to talk about cereal, monitor Facebook/etc for cereal ads for X hours, then under similar conditions

Or just plan a topic and a survey period. Eg if we're going to talk about cereal, monitor Facebook/etc for cereal ads for X hours, then under similar conditions (time of day/etc) after you talk about cereal for a while. To be ultra paranoid i'd avoid even chatting about it digitally. ISP distrust.