For this to work, we would need a few different things:
1. A practical use and need for the land.
2. A way to protect the land.
3. A way to protect ourselves.
The first thought for using the land is residential. But I don't think that's practical in our lifetime. There's still plenty of undeveloped land on Earth, so we aren't running out anytime soon, and to support a large population on Mars I think you'd have to terraform it to some extent, and that technology won't exist in our lifetime. Another use of real estate is harvesting natural resources, but I don't think there's any valuable natural resources on Mars. Manufacturing sites would be impractical because you'd have to sustain a shipping line. There's no way for that shipping line to operate in stealth, and it would be too hard to defend against jealous governments on Earth at our points of ingress and egress. I think our best option for making the land useful is to build data centers. Since they'd be off-world, they could operate free of government oversight. We'd have to build a mostly self sustaining infrastructure of robots that can manage the data centers.
To protect our real estate on Mars against jealous governments and corporations that will eventually realize what we're doing, we'll need an army of drones that have plenty of ammo and good deep learning AI algorithms to respond to threats. We'll want very maneuverable ones, like the quad copter drones. It would be hard to protect against a nuclear strike, so we'd need to operate at just the right amount of profitability and damage that it won't be worth the expense to jealous governments to send large nuclear payloads to Mars. Maybe we can also protect the facilities better by building many of them underground.
To protect ourselves, we'll need to remain anonymous and rent out the real estate on the black market. Then we'll need some kind of business front for money laundering. I hear car washes are quite effective.
