James Bond 007 Blood Stone

A reach over takedown counts when an enemy is directly opposite you behind cover like box, the thin covers dont count towards this achievement you just have to hit X and you lean over and drag him over the cover. If you cant do this until you complete the game just reload the checkpoint "Bangkok 3.4 old friends, new enemies" this is the best place i found to do it, just do it in the first cop, restart checkpoint, rinse and repeat.

On Istanbul 1.1, after you have cloned the 3 computer hard drives, and after you go through the cut scene of dropping the trailer....

The game sets you up to get a stealth takedown very easily.
Just hit X at the prompt... and you get one stealth takedown.
Go back to reload checkpoint and you will have to sit through the cutscene again. Rinse and repeat as many times as necessary

Note 1... After 1 serious playthrough of the entire game, I only had about 7 stealth attacks so recycling this clip was the easiest way for me.
Note 2... If you haven't gotten the knock 5 villains off the balcony
"Free Fall" achievement, this is a great opportunity as there is a guy just beyond your stealth kill guy who is conveniently waiting near a ledge. Just softly walk up to him and press X on the prompt.

Good luck!

The best part of the game if you just want to rinse and repeat this is in the Monaco casino gardens just before the third and final security camera. There is a checkpoint then you walk down a set of steps and round a corner to your right, two guards are talking, on the far side of a low wall. Wait for one of them to step forward, then do a stealth takedown over the wall on the one closest to you. Immediately hide behind the wall. The second guard will turn around to look for his friend who seems to have disappeared, and walks close enough to the wall that you can grab him too for a second reach over cover takedown. Then just reload the last checkpoint, which is immediately before this action as often as you need to.

Cover takedowns are when you press A to get up to a wall, and an enemy is nearby(makes it easier if they don't see you). Let them walk slowly up to you, and when they are close enough, it will tell you to press X. Make sure you don't stand up or get out of cover before doing this!