Each course has four holes. Zombies are killed by any contact with the ball, so there is no real need to hit the ball hard or use the effects of the perfect shot (though that would help). All that is required is to use as many strokes as you can. Aim for a relatively long shot and land in front of a group of zombies so that the ball bounces and rolls forward into them. Take three or four shots a hole and kill two or three zombies per shot and you will have no problems. After you kill thirty throughout the four holes the achievement is yours.