spikes are worthless. They get destroyed easily with each hit. Archers take them out quite fast. The best ideas is to try the Masada approach. Build up the land to stark cliffs high atop you can put normal buildings. This is not unlike many medieval fortifications. Use a narrow spiral ramp or stair up so trolls stay low and you can shoot down on them. Then you can put a murder hole to shoot at the gate where all the bad guys congregate.

Unfortunately there is little defence against flying drakes. The game has not invented anti air gatling guns yet. But the good news is a few fire arrows takes them out fast But then you did not want to hear about this.