Sniper Elite 3

If an enemy spots you, you need to move (Oscar Mike = On the Move) and you'll be told to relocate. Do this 100 times.

You can grind this out while playing a solo challenge. Here's how.

On a couple of levels a tiger tank will turn up. Take out every enemy on the map except the tank. "Enemies" should be '1' - just the tank.

Now place a land mine the middle of the road to incapacitate the tank.

This is where the fun starts; run out to the tank so it sees you, when the detection circle turns red start to run away, and you'll see 'Relocate' pop up. keep running away from the point you were spotted until the distance reads 0 M. At this point you will have successfully relocated. Now go back to the spot where the tank saw you and repeat until you get the cheev.

Here's a video I made from the X360 version http://1drv.ms/1ruZZ6E

Note, every once in a while you might get shot at by the tank, so you might need a couple of med kits or bandages.

When the enemy spots you, you will be told to relocate. This means getting away from the enemy that they lose sight of you. In the bottom left corner of the screen is an indicator that you can use to determine how much distance you you need to get away from them. You will be relocated once the indicator goes away. The indicator only appears when you have been spotted.

What counts as a relocation
A relocation counts towards the achievement when:
1. the "relocation" bar next to your mini map has started filling up to any degree
2. you have emptied the relocation bar by moving to a new position

You do NOT need to be discovered, fill the bar all the way up, nor see the "Relocation successful" prompt for it to count.

What fills the relocation bar
If you fire one detected shot (either by sound, by making a wounding shot, or that an enemy sees someone go down), it fills up 50% and enemies could eventually come searching at your position. Fire another shot, and they're likely to come searching at your position directly. Fire another shot, and the bar will "overfill". If an enemy spots you, it will also "overfill". When the bar overfills, enemies start shooting and advancing at your position immediately.

Grinding the achievement
This means you can just fire one shot and relocate, fire a shot, and relocate. You don't even need to have enemies in close vicinity, as long as any enemies are still alive on the map, firing a shot will start filling up the bar. So if you wanted you could just run around a map firing shots in the air every forty meters and you'd eventually pop it.

Relocation as a ridiculously OP tactic
Rather than grinding it, I'd recommend using it as a tactic. It's ridiculously OP and cheesy, especially for Authentic difficulty. Kill one (or two) enemies, move to a new position. Repeat.

Just retreating works, or moving back and forth between positions. If you are far enough away from any nearby enemies, they won't ever advance at your position. If you can hear them say voicelines like "Don't move, let him come to you" you're pretty much safe and can just keep picking them off like ducks in a barrel; Kill one (or two), move 40m, kill one (or two), move back to original position, repeat.

Otherwise, place a few traps close to your location and make sure you always have a safe place to retreat further back to if they come find you.

This tactic makes some levels on Authentic pretty much trivial, as long as you're skilled at sniping reliably from a moderate distance.