Ok here's what I did:
First on this scenario I was messin around with (from scratch) I made this trigger where if my enemy enters a certain area, they'd convert to my team (Change ownership). I kept testing and adding and stuff but when I got to the point where I thought I should start damaging em with something, I used enemy seige onagers. Look at the chart-
O=Change ownership area
X=Enemy Siege Onagers
*=Gaia rocks
***************X*************
**********************X******
OOOOOOOOOOOOOOOOOOOOOOOOOOOOO
OOOOOOOOOOOOOOOOOOOOOOOOOOOOO
OOOOOOOOOOOOOOOOOOOOOOOOOOOOO
OOOOOOOOOOOOOOOOOOOOOOOOOOOOO
OOOOOOOOOOOOOOOOOOOOOOOOOOOOO
If the siege onagers would fire at the Change Ownership area, those fire ball things that they shoot out turn grey and freeze in air and wiggle. Yes they just remain in the air frozen but wiggling and twitching. Now I hope this wasn't discovered yet.