Easy Reaver Kills Cheat for Gears of War 2 on the Xbox 360

When you're directly underneath the Reaver, it can't hurt you, so you can just pound it's stomach until it dies (the death explosion wont hurt you either).

Reavers also have more armour on the sides and top than on the stomach

Just try to clear out the other enemies that can still shoot you while you're under the Reaver before running under it.

This strategy works on most of the Reavers, even on insane.