According to some alkthrough you should avoid the Obelisk in C&C:Renegade until you disable the Power Plant from inside of the Power Plant.
Otherwise you can NOT avoid the Obelisk, as that has 360 degree instant attack (and instant destroy on anything but the most heavy units) on any ground thingy.
This is the exact problem I talked in my game, where you can not even disable the Obelisk by destroying something else (as far as I know).
The original game by the way is accessible on
Abandonia!