Once you have a few Caltrop Bombs (either by crafting them or buying them from a black market dealer), look around for a scaffold. I found a lot of scaffold around the docks area in the Galata District.
Once you have located a scaffold find some nearby guards and piss them off so they are chasing you. You will carefully have to throw your bomb down so they are "stunned" in the front of the scaffold. Once they are stunned, you will have to run using RT and by running parallel to the front of the scaffold, once you get to the edge of the scaffold you'll have to press b, make sure you untarget whom ever you have targeted as the game automatically targets someone that was stunned by the Caltrop Bomb.
This process is tricky and I recommend you testing it out first. Also please check out the posted video as it shows you how to do it because it is harder to explain verbally then it is to physically show you.
It is a cumulative total, I know this first hand because I had four deaths on my first scaffold and on my second scaffold (consisting on three deaths) the achievement pop'd.
OG Gary Goonie: "i stood at the scaffold and shot the enemy, just to avoid the chase sequence."
Thanks for the addition
Props to YouTube user PowerPyx for the video on YouTube.com