On paper this sounds like a cool idea, but in practice it just doesn't work for reasons that have been stated above:
They're discount 187th / DU / Shock / whatever else
Too many regiments / battalions already.
But I think that everyone misses the point that this post has brought to my attention. Personally, i believe its up to every trooper / battalion to guard the base and maintain its security. If not everyone then at least Shock, which I have seen them do from time to time, because its kind of their thing to guard things etc. But more importantly, I'm pretty sure there is a document or sheet out there that has all the battalions down for a certain time per day to man either the base defences (walls etc.), Alpha outpost, Bravo outpost as well as just general patrolling. (I know that 104th and Rancor have this document but i'm not sure about the other battalions.)
So an easy fix for this would be to just follow the schedule provided as closely as possible. But this would have to be enforced by BCMD+ in every regiment / battalion.
TL;DR: There are already Battalions on the server that does the Job of the "15th Defence Core" *cough* Shock *cough* plus other Battalions can do the Job of the suggested Battalion. There is no need for it.
Sorry Chief, but its a -1 from me