Two such structures can be seen in this photo of the Bitchu Matsuyama castle. In the front, the yagura turret features on two sides a sort of wooden skirt, a rather obvious ishi-otoshi. A better camouflaged one is visible on the main tower, at the base of the first floor's window.
EXIF info:
Nikon D700
Lens: VR 28-300mm F/3.5-5.6G
Focal Length: 78mm
Aperture: F/7.1
Shutter Speed: 1/640s
ISO Sensitivity: ISO 400