main-base-invulnerability

In the blueprint "concept", it is stated that the main base should be invulnerable until all minor turret bases have been destroyed.
An alternative to that, could be that the main base is protected by a series of forcefields and "laser walls", controlled by some power stations, which have to be destroyed to shut down the "laser walls" and forcefields.
In addition to the power stations, each team could have some turrets placed at strategic locations, which would not necessarily have to be destroyed in order to damage the main base.