This trick will only work against some kinds of patrolling - works on enemies patrolling in the same spot, but won't work on enemies using the circular patrolling, or even irregular or big patrollings (in more than one place). You can  stop any unit from patrolling, even shamans. All you have to do is place a tower plan right where those units are patrolling - if it doesn't work, it means you placed it in the wrong place, so delete it and place another tower plan on another nearby square. This tactic is cheap and is banned from the PopRE matchmaker.