Aggressive mobs cannot pathfind around dripleaves, I waited 60 seconds, while moving around and the zombie couldn't move, as shown in the video, there are two ways to do this shown in the video.

EDIT: video exceeded the limit so made a google drive link, 

https://drive.google.com/file/d/1paZs1Kfbd4xpaGqI710Tw_qaP78C7R0R/view?usp=sharing