Jerk Cord's ideas are nothing new to duck hunting decoy spreads. Motion decoys are critical to duck hunting and you can ask any serious duck hunter only to find that a jerk cord is a staple to the sport. Much great pre-fabricated jerk cord or jerk rigs are out there today, but if you want to build one that is super lightweight and packable for about $10-15, check out this short video from Jason Cruise, producer of Mossberg's Rugged American Hunter series.
Here's a little secret: use para-cord or what's often called "550 cord" for your jerk cord or jerk string system. Why? It doesn't tangle and kink nearly as bad as other ropes do, and it's easy to untangle if it does because it's thicker than your average pre-fabricated jerk cord system.
A jerk cord doesn't have to be complex, but you have to think through it. This strategy uses PVC pipe to build the jerk cord and allows for multiple water depths to create motion decoys on a simple budget.