There's an easier place to get this achievement :
Start the "Heat" trial instead of "Playground"
As soon as it starts, look ahead to your right, there's a plank, a wall & finally a fence (without barbed wire)
Now run on the plank, wallrun (lb), jump (lb), hit LT once above the fence, and push LT as soon as you land. You should get the achievement.
I'm not sure but i think "heat" is unlocked after finishing it in Story mode.