Prevent Instant Build, while under siege/contest.

[Liatni 35]

Too many times,  people can spend time blowing down a gate to get in and before they can even take a step, another gate is tossed up. Same with, clearing out a  battlement, cant progress forward because, defenders will just rush in, put down more walls and a bed and.. you name it.     Think, maybe repairing (that can be interrupted), instead?