The future is a terrifying place. Atmosphere-capable ships can rupture your lungs and cause you to drown in blood through pressure waves. Their weapons can destroy you from orbit. Asteroids can be towed and dropped, rendering planets tombs. People have a vested interest in keeping hostiles out. In almost all cases, defences will be connected to an overall defence grid with several limited AI co-ordinators and fail-safe systems. These defensive systems are in addition to the protection afforded by standard orbitals and patrolling ships. The following measures are in a roughly ascending order of rarity.
MPDO - Multi-Purpose Defensive Orbitals are technically capable of turning their guns on ships, but their main purpose is to intercept and destroy asteroids, whether they be on a natural collision course or guided by enemies. They are relatively fragile and wouldn't do much against a cruiser-class ship.
GODL - Ground-to-Orbit Defence Laser systems are simply ship weapons mounted in terrestrial bases. They can be obscured somewhat by natural features, such as under oceans. They are cheaper than OODLs, and allow for larger weaponry whilst retaining these savings due to the terrestrial power infrastructure.
Orbital Mines - Orbital Mines are incredibly simple craft, functionally a passive sensor and a payload. Once the passive sensor is tripped by an activation signal, the mine detonates. They are very hard to distinguish from space-debris due to the complete lack of emissions. Many are camouflaged as such to further hide their nature.
OODL - Orbit-to-Orbit Defence Laser systems are simply ship weaponry mounted on a more compact orbital satellite. Due to lacking the advanced FTL propulsion they are somewhat cheaper, although obviously less mobile. They are significantly more expensive than GODLs.
ODHN - Orbital Drone Hive Networks are limited AI systems housing a huge number of self-destructive drones which scream towards enemies in distributed swarms. The payload carried varies, and the AI is more than intelligent enough to match up the ideal drone to the target.