I made the same spell without any triggers, based solely on Rain of Chaos spell. The problem is these towers' initial animations right after appearing on the map are all under construction. They only change their appearance to normal (full building without constructions) if they have something to do (attacking, casting spell). And when the spell's duration is over the towers explode like they were destroyed which is not logical (perfect sequence should be they disappear out of the map with an animation of teleportation - but I don't know how to do it.)