i just have a quick question in alot of zombie maps Raccoon city for example the computer attacks the barricade aka siega tank own
by player 12 regardless if a human player fires at them which gives it more of a barricade effect, how would do this?

i opened the map and there was no trigger that i could find that explains it, unless i missed something?

It's not player 12. The tank is owned by a computer player colored dark aqua.

Edit the color in the Map Description

Unally the computer with P12 (set alliance status: P12 to Enemy). Use ground attacking units as barricades (then the target won't be changed).

Or have the barricades owned by another player that is unallied with the enemy and give the barricades to neutral afterwards (zombies will attack p12's units, if their old owner was the zombie's enemy).