Maybe I didn't explain it right.
Let's create an example, I have a code that displays an ad every "X" topics (let's assume it's 3).
KEY: {advertisement="title_topic"}
Now let's assume that I have 4 active ads.
The problem is, out of these 4 ads, the system may end up showing an ad repeatedly as it is random.
Is it possible to force it not to duplicate an ad?