The computer usually sends the harriers to attack your ore refinery and when u kill them with your patriot missles (allies) or flank canno n(soviets) they still come down and destroy you. Find out witch direction the harriers are coming from then build an MVC or move your main one to where the harriers are coming from. Leave a big space to let them crash then deploy your MVC build at least 5 patriot missles (allies) or flank cannon (soviets) in a row then move your MVC out of the crash area. Voila! no more worrying about harriers!