Need a Hand? Achievement
Need a Hand?5
Prevent a Walker from Damaging You by Severing Its Attacking Limb
This can easily be done with a gun or any axe type weapon. To make this easier shoot off of cut off one of their arms so they only have one viable way to swing at you. Once you've done this go in to bait and attack and when they swing pull back and shoot/chop off the arm.
You may actually grab this achievement naturally in your journey through the game.