What was the actual stockade?

The actual stockade is what civilians would call a jail. Most bases have one.

In the "old days" there were two jails on most Army bases. The stockade is like a county jail: if you do something bad enough to get sent to jail, but not bad enough to get sent to a prison like Leavenworth, you go to the stockade. The other was the Correctional Custody Facility, where people who needed their act straightened out in a hurry could be sent for two weeks of abuse. Those were closed because most bases used (I can't use the term for what these people were here--think "jerk" but worse) sergeants from the units as the cadre for the CCFs, and they were killing people.