Trigger Help

I am making a map similar to that of Fortress Survival where the creeps go around the map looking for players. However, I don't know a trigger that would do this? Any suggestion?|||Use regions that when units enter it, they go attack move to an other region, when in that region, they go attack move to an other region, etc. etc.

Here is a very nice tutorial about something very similar;

http://war3.incgamers.com/forums/sho...22&postcount=2