Here's a way to make an almost - Command and Conquer: Tiberian Sun
Here's a way to make an almost indestructable base. First go to skirmish and put the tech level to 10.
Then build a NOD or GDI wall that surrounds your base. Then if your using NOD set up a LPF (laser Powered fence)make sure it's powered.
If GDI set up a Firestorm wall around your base. Then put a wall inside your other wall barries.
Remember to put Automatic gates so that your units can travel in and out your base.
Also remember to put lasers or any other destructive devices outside your wall.
I always do this and it has never failed me yet