This temple model here has a pre made 'weak spot'. There was a taught cable rigged through and the stones were carefully repositioned so as to make the temple look solid. A special heavy bolder is rigged with the wire running through it and this is then thrown at the 'weak spot'. When the bolder is thrown, it runs down the cable and hits the desired point every time enabling many re takes. The beauty of this idea is that the camera can frame and focus on the known position of where the bolder hits rather than just estimating and it can be shot time and time again.