I found that the 2nd level in the campaign was a good place to get this achievement. You'll be fighting against Starbright in this level. It really doesn't matter which army you use. I think the easiest way by far to get paybacks is wth the anti-air turret. There will be 2 waves in this level that have flying enemies. Have one anti-air turret built and ready by the time the 1st flying enemy wave comes. Don't build a second because it may steal kills from you. You will be using the anti-air turret manually. You can only get paybacks when manually using a turret. There's a good chance some of the flying enemies will hit some of your other turrets before you shoot them down. You can only get a payback if the enemy has hit one of your turrets prior to you killing it. It's quite possible to get all 10 paybacks in one level. That's what I did.