Fighter Base PDCs are your friend. As I posted recently, they make great cheap defenses on perimeter colonies to keep the locals feeling safe. Build some prefabs, and drop the prefabs and a smattering of minerals on the new colony (along with some construction brigades if you have no factories), then use a pocket carrier to transport a squadron to their new backwater posting.
Fighters don't require mineral maintenance costs the way picket frigates or monitors would, they're more flexible than a laser PDC, and require less logistics than a missile PDC would. I usually build a small barracks into the PDC as well, so I can house my Civil Affairs Battalion (read: Garrison) safely as well.
For major worlds, I do a combined fighter/missile PDC with larger troop capacity.
Example:
Wright class Planetary Fighter Base 45 350 tons 80 Crew 3934.9 BP TCS 907 TH 0 EM 0
Armour 14-113 Sensors 1/420 Damage Control Rating 0 PPV 42
Intended Deployment Time: 0.1 months Flight Crew Berths 6
Hangar Deck Capacity 18000 tons Troop Capacity: 5 Battalions Magazine 171
Fuel Capacity 500 000 Litres Range N/A
Big Bear Silo (6) Missile Size 7 Rate of Fire 55
Stanger-Hercules PlanetGuard MFC Mk I (1) Range 352.8m km Resolution 100
Big Bear Anti-ship Missile (24) Speed: 14 000 km/s End: 183.3m Range: 154m km WH: 18 Size: 7 TH: 46/28/14
Stanger-Hercules PlanetGuard DRADIS Mk I (1) GPS 42000 Range 336.0m km Resolution 100
Strike Group
40x Cobra Fighter Speed: 4090 km/s Size: 8.8
Missile to hit chances are vs targets moving at 3000 km/s, 5000 km/s and 10,000 km/s
This design is classed as a Planetary Defence Centre and can be pre-fabricated in 19 sections
Bear in mind that this is a considerably larger base than I'd use for a backwater world, since it holds 4 squadrons of 10 each. A much smaller PDC with a 10-fighter contingent and without the ASMs would be ideal for those.