A small device, the size of a grain of rice, is implanted in a number of individuals to track their movement. These individuals are usually compliant but being tracked is also not exactly in their interest. For this reason the organization decided to place the implant in a body part that makes extraction difficult/dangerous at least for an amateur. On the other hand they do not want for the set up procedure to be too much of a hassle.
What is a good place in the human body for such a device? Insertion should be possible without anesthetic (local is allowed) and treated individuals should require no hospitalization. Location must not pose a threat over long term and limbs are not allowed.
EDIT: My question is hardly a duplicate of the provided question. That question revolves more around security features and NONE of the answers provided deal with the location (what I asked) of such a device in any meaningful way.