Throughout a dictator's reign, what type of schemes might his advisors engage in without his knowledge?

The most suitable choice would be "Secret" because often in the context of a dictator's regime, advisors might pursue schemes that are clandestine or hidden from the dictator. This aligns with the idea that in oppressive regimes, advisors could operate with their own agendas, which they would not want to disclose to the dictator for fear of repercussions or losing power. Such secretive schemes are typically rooted in the necessity of maintaining the status quo or advancing personal interests, making the element of secrecy crucial.

The other options don't fit as well within this context. "Occult" implies a connection to the mystical or supernatural, which does not appropriately address the political and strategic nature of schemes in a dictatorship. "Open" and "Visible" suggest a level of transparency that runs counter to the common dynamics of a dictatorship where trust is often lacking and subterfuge is more prevalent. Therefore, "Secret" is the most fitting answer.