I thought about an easy version with boxes of different sizes hanging with the string and balloon, but that may be going a bit too far. I have also read about using different colored helium-filled balloons staked to the ground in a loose cluster with instructions to shoot certain colors without hitting any other colors. This is, from what I understand, useful for police marksmen in simultaing hostage situations because the wind keeps the balloons moving in random patterns.
Sorry, don't want to start a thread drift already. One of the things I love about this crowd, versus other forums I'm a member of, is most here seem to understand that we are trying to stop an assailant as quickly and effectively as possible and not necessarily kill, incapacitate, wound, or any other particular term. Obviously, the quickest way to stop an assailant is to completely incapacitate him or her with a bullet or fifty to the brain. This may or may not be possible depending on the situation.
Shooting high chest gives the best possible chance of striking heart, spine, lungs, and of course hitting the thicker part of the sternum. Hitting this part of the bone has a chance of creating multiple additional projectiles in the form on bone fragments. While not as quick as hitting the brain, the onset of hypovolemic shock will happen much faster in this artery-rich area than in the lower chest or upper abs.
I also think the idea of trying to take out the pelvis with a frontal shot as a failure to stop drill has pretty much been disregarded by most, hasn't it?