Re: GPS tracking in guitars...?
Years ago Micron made a GPS chip for tracking but it was cost prohibitive. It was about $500.00 per chip, then you would need the tracking hardware also (in the four digit range - $,$$$.$$) It was intended for larger, industrial use, but I had considered in certain equipment that was high enough value I could not replace. It was able to find an object across state lines. Couldn't fit it in the budget, however.
Nowadays there's all kinds of GPS tracking devices from China, but I can't tell if they are suitable for tracking stolen goods that are out of your possession.