My pirate safe haven runs gambling rings, horse races, and trades contraband but no one can find it or penetrate it. Why?
I've got a story revolving around pirates and a rescue. The pirates have a large organization and hide in a haven like the Barbary Coast. In addition to piracy, they bring in rich people to gamble and run numbers, do many corrupt activities. But the location remains in an uncharted region.
I want the haven protected from being found out, and from being overrun if they are found out.
The world is unique. It is post-apocalyptic steampunk, with a single government per this question, and there is no sky, so celestial navigation is out. The region is dessert wastes of an alien planet, so landmark navigation is out. Civilized society uses radio beacons and lighthouses to navigate. There are no lighthouses marking the areas by the haven. So, keeping hidden is pretty easy so far. But:
Trading/Gambling: The pirates run many money making schemes such as horse racing, playing numbers, casinos, and dealing contraband. So civilian crew are reaching the haven; the pirates only allow you in if you let them pilot your ship, and your crew stays below. No one gets to see how they got there.
Generally, the pirates can feel safe with this arrangement, but the Captain is paranoid. It's a matter of time before some large navy comes rolling in to try to shut them down. Relying on hiding alone won't do.
Why wouldn't a small navy be able to penetrate the haven?
I need to lay the haven's defense perimeter out in a way that protects them from a sneak attack by a single small navy of the civilization, which consists of five well-organized and maintained cities. I originally went with a walled fortress, but that stopped making sense because it's so easy to spot from a distance. Then I got stuck, and this question came up.
The world is 19th century tech in a post-apocalyptic wasteland. Food supplies don't exist outside artificial habitats like cities or this haven, so time on a ship has serious logistic limitations. Fuel is everywhere however, ore is mined and it reacts with the toxic air to release plenty of energy. This powers everything from their engines to their air conditioning, and electricity.
It is steampunk, all ships are airships. There are no seas. If attacked the navy would be using small, quick frigates with light guns designed mostly for ship-to-ship battles. They would bring a couple "long tom" big guns, which could do a lot of damage to only a few targets (they have to choose wisely). They would be so far away from support that a battle could not last more than 3 days realistically. That would only change if the navy dragged out a floating battery or resupply ship; which would quickly become targets they would need to defend. Generally not a net benefit.
Pirate ships are evenly matched with the navy; mostly frigates. There will be fewer of them and crews will be not as well trained in naval combat. So the haven needs to offer support.
Cannons can be mounted on turrets or towers. Big cannons are slow to load and slow to aim, difficult to hit a running frigate. But they are the only thing with stopping power because smaller weapons don't do much damage to gas bags. A well-placed cannon round can knock out a whole section of the gas bag, and it has a medium range of effectiveness.
Trebuchet has multiple sharp spears that hope to break windows and contaminate an intruder ship. Very short range and the shot scatters randomly.
Fouling shot has a long length of cable wadded into a cannon. It spreads out in the air and hopes to foul any ship screws or engines. Really just luck, you can't aim one. But a fouled ship is a sitting duck.
Walls have limited use except in the event of some ground vehicle attack. Anything like this would need to have the vehicles carried in by airship because there is little hope of crossing the wastes. Walls can reduce the effective range of long range weapons, and prevent ships from targeting whatever is behind them.
Camouflage would only be effective in hills or low mountains. The only way to hide in the barren wastes would be to look like a mountain. Or a big rock. They don't have the tech for big cammo; or at least, finding a real set of hills would be cheaper (and cheap is good for greedy people)
Lookout towers can be manned, but it's horrible work, and the guy you send there will likely be unreliable. Probably something you just leave empty until an attack is suspected. They can radio signal back to the haven.
How do the pirates use these tools to defend their haven?
A good answer roughly paints a perimeter with these tools that a small navy won't get through. The answer is a worldbuilding answer, so limitations on the navy beyond what I gave are fair game. However, the assumption is that a small navy can reach the haven and carry out a battle for three days, but What enables them to hold off the navy?