Yes... what Zach said is probly best.. All you gotta do, assuming that you don't have hyper trigs, is:
Condition: Always
Action:
RunAiScript - Random Suicide Mission
Wait - ??? .. maybe every 5-10 seconds or so.. so 5000-10000 milleseconds.
Preserve Trigger
What this would do is make each of them randomly attack an enemy unit... Therefore, some of them will attack the barricade, and some of them will focus on the players, even tho they can't reach them...
If you want to make sure that they focus on the barricades completely when no players are next to them, then use both Random suicide mission and patrol...
so it'd be...
Action: RunAiScript - Random Suicide Mission
Wait - ??? .. maybe every 5-10 seconds or so.. so 5000-10000 milleseconds.
Order - all men for current player patrol to location x (which would be where the players are)...
Wait - ???
Preserve Trigger..
So this way, they'll randomly attack... and then focus attack on what's ahead of them (if players are next to the barricades, they will try to attack the players since Patrol AI will make them attack higher-threat units.. [which are units that attack them])... and then they'll start randomly attacking again....
Finally, you can make the zombies focus on the players when they're close to them by having two locations.. Location A, which will be Bigger.. and Location B...which is smaller, both centered on a player..
So what you do is this:
Trigger1:
Conditions: Always(?)
Actions:
Move Location - Move Location A on Terran Marine (?) owned by current player
Move Location - Move Location B on Terran Marine (?) owned by current player
Preserve Trigger
Trigger 2:
Condition: Computer (zombie force) Brings at least 1 men to Location A
Actions:
Order - Order all men owned by Computer (zombie force) to patrol from Location A to Location B
Preserve Trigger.
This would make them selectively chase the players that are close to them.. but it isn't really necessary, as random suicide will also chase selective players, but it may not choose to kill the one right next to them...
Remember that this will not work with Hyper Triggers, as it'd continually make the units patrol to Location B so quickly that the zombies will not have time to stop and attack the players.
If you ARE using Hyper triggers.. then use deathcounts.
None.