It has occurred to me that every democracy or republic is bound to eventually become dominated by their own intelligence apparatus or "Secret Police". This is usually after some sort of catalyzing event that introduces some kind of executive or bureaucratic apparatus (which in the USA happened with the constitution).

Basically the concept is this. Let's say you have two groups - one is elected by some kind of plebiscite (and are thus incentivized to be 'electable'). The other group is appointed by these elected 'representatives', and their term is only limited by the whim of the elected official. Their incentive is to either a) Lick boots so well that the politician sponsoring them wants to keep them around (which is a flawed strategy - once a rival is elected instead of your sponsor, expect to be sacked) or b) spend all of your time compiling blackmail material on the current elected official with the power of employing you AND compiling blackmail material on any potential rivals to that elected official's spot. Of course, once you start going down path B, you may as well start comprehensively blackmailing everyone in government and everyone that has the potential to undermine your government, so that you can acquire more actual power for yourself (and for the cronies you now have forced the elected officials to appoint). Generally, this seems like a solid strategy, since reputation is important to the person getting elected, but not at all important for the blackmailer.

Now, what policy alternatives are available to curtail this or change the incentives? The most common thing tried by elected officials is to outlaw blackmail, but that does not actually change the incentive structure, since the blackmailer will simply release the material anyways to sink you if an elected official were to have anyone make the arrest. It is more sensible to 'go along to get along' in that scenario (incentive-wise), regardless of the legality of the situation. This in fact amplifies the power of blackmailers, as those 'going along to get along' are in fact now conspirators in a crime to cover up the blackmailing of themselves and likely others (may as well make a deal to blackmail your rivals so long as you are 'going along to get along'). Another example is abolishing bureaucracy, making all public power wielded by elected officials. This will curb the blackmailing by their own apparatus, but there may be other sources of power that operate under the same incentive to blackmail. Unions, cartels or any other sort of legal monopoly granted by government in the private sector also are incentivized to either a) Lick boots (most commonly via bribery) or b) to blackmail politicians to get their way.

Dang. So there's really no way to avoid this so long as the government wants to have control over either a) it's own agents (by having bureaucracy) or b) the private sector (via monopolies or other privilege grants to special interest groups). So what is the way to solve this? Easy - abolish the government. After all, the only reason these guys got elected in the first place is because some group(s) banded together to use force against anyone not in their group (see Oppenheimer). That's why they want control and need agents doing their bidding, whether in the public or private sector. Thus, all democracies/republics are doomed to this fate, as it is a model designed to incentivise this. Considering that these systems seem to be sticking around for a while, I would posit that this was likely the point from the beginning - that the representative aspect of the system is ultimately a smokescreen for what is in actuality, rule by blackmail.