How about adding 1-2 automatic/manned Sam-Site Phalanx Turrets to each small outpost? It could be added as a benifit for owning an Amp Station. So without one, the shields on the turrets are down and the turrets would not work at all, or would require a gunner.
The shield would be directional, so air with some level of co-ordination could take it down.
It's range would be about 50-150m, and it would have clips with 4 missles. It would require the user to keep LoS and one clip should deal about 1/4th of an ESFs health. It's reload would be 1.5 secs short and 2 secs long.
So what do you guys think?