KadeWiedeman

This may seem a naive question if there it's an obvious answer, but how does one build multiple of the same structures (I.E guard towers and sandbag walls) on a territory? I have come to hear that this is possible, but is it only possible in lvl 100+ territories? I only just achieved my first today and plopped a single sentry down on it, so I don't have much experience with the mid-game mechanics.