Whilst playing the Shi No Numa (Zombie Swamp) map, various places around the level will have boarded up area's designed to keep zombies from coming to get you, except it doesn't actually stop them, it just slows them down.
When a zombie removes a board you will be able to put it back up again by holding X near where the boards were before they got knocked down. You will do one board at a time so it can be a tricky one to get.
The easiest way to boost this is kill every zombie in the first round except one, let him tear away at a window and then you stand next to it and hold the X button to put it back up. Be careful though that he doesn't reach through the barriers and try to grab you as this will hurt you but you can easily step back if this happens. Just keep repeating this method until it unlocks.
If you want to get this legit then my advice is to board as many windows as you can up between rounds - make this your main objective if you are solely going for this achievement.
Another good tip would be to allow the first few waves of zombies to completely tear down as many of the boards as they can - because the first few waves are always relatively easy, you can board them up as you take them out and afterwards.
Finally, if your at a point where a lot of windows are unboarded and you are certain that there is only one zombie left, allow him to follow you but don't kill him... this way you can go and board up as many windows as you can before taking him out and carrying on.