Hypothetically if you had to design a checks and balances system for a minarchist government to attempt to prevent it from growing beyond it’s originally intended scope, how would you design it?

Here’s the scenario:

Some minarchist libertarian forefathers are drafting the frameworks of the government they’re setting up on some island. For whatever reason, you as an ancap are tasked with creating a “checks and balances” sort of fail-safe system for their government to help ensure them it won’t get out of hand. Maybe they just thought an ancap would be the best person to consult with about this prospective problem.

The point is to attempt to prevent it from being able grow beyond it’s original intended scope of authority and function in the future, no matter what. The government is only being set up to socialize 1 or 2 small services, and to police murder and theft and that’s it. As far as minarchys go it’s not too bad and people are barely taxed, and victimless crimes aren’t being patrolled on the streets for.

As for the structure as it is written already, there is no official “legislative branch” because these minarchist forefathers, as I mentioned, don’t want the government to grow and at the very least they are smart enough to understand that baking in the capability for adding more legislation is a no-no.

Your answer is NOT ALLOWED TO SHRINK OR DISMANTLE their government though. It has to be a solution that keeps their government intact and focused on it’s initial purpose, while simply retarding it from metastasizing into a cancer on earth in the future. It’s just a thought experiment, and I know it goes against our instinct to support such an idea of helping some statists set up a state in real life, but it’s just for fun and I’m curious what sort of solutions would be presented.

Realistic tech based answers are welcome too, such as AI sentry turrets aimed at the president 24/7 where all citizens have access to a red button app on their smart phones and if 80%+ press it the president gets turned into a red mist… as long as your answer is possible with MODERN technology and not too sci-fi/fantastical. Thanks for participating.