You can delete enemy tower plans by placing a tower plan right on the same place as the enemy's plan. This trick only works with tower plans. You can easily see where a tower plan is by going worldview. Using the "build in worldview" trick can help you suceed on this one too. This works both offline and online, but is a banned tactic in PopRE matchmaker, since it is considered as a coward move to delete plans and avoid the enemy from building towers.