Protecting Civilians for their own good?

[Lunaticus (OP)]

After playing some more I am a bit stuck and would be thankful for some advice. 
I expanded a bit through the solar system and set up some colonies in the surrounding system.  They are still rather small (1m max population) and are completely dependend on Earthern support.  In order to facilitate things I set up Jump-Gates to the systems (which might have been a mistake).
All of a sudden in one of the system some really nasty Alien race showed up and started to kill the freighters moving infrastructure to the local colony.  Now I understand that in the galactic map some red values come up to signify the threat level of the system and nobody went there for a couple of years.  I also cancelled all civilian contracts for the local colony.  However now after maybe 2-3 years the threat level is gone and the civilian companies tried again to fly towards the colony and got killed again. 
So I am wondering if there is some permanent way to forbid a system to civilian shipping lines? I am aware that there is such an order as "ban body" which however only works if I do not have a colony there? Or is my only way to keep my civilians from killing themselves regularly to abandon the colony? My preferred option would be to leave the colony as it is until my technological capability is good enough to fight the Alien menace but to make sure nobody flies into the system.
Any advice appreciated.

[UnLimiTeD]

you could build and sacrifice a cheap ship to raise the threat level, you could use SM functions to delete the Jump Gate, and banning the body is possible as well. It doesn't always work enough, but I think it should overall.