My jacket has a pocket designed for carrying an extra shield...works great. Fits under the right arm from chest to back. I've actually carried an extra shield nearly in the same location without a pocket in the past before I had this jacket...never any issues...can't really fall out with a zipped up snug at the waist jacket.
The jacket is the Joe Rocket Reactor 2.0...other colors available but mine is red to match my bike...