How is it going to mark the individual elements that are stacked? For example if a red triangle is on 65 adjusters will it highlight ones with stacking problems? As with other games with building, your detection of overlap has not been perfect. If a single player places one element, say a container, then places other elements next to it, there is always a chance that if you put the original element in edit and move it and move it back, it will 'think it can't be placed'. This should never happen.