security solutions

i am looking to see if it could be possible to build a contraption that could help in combating hostage taking in my state. we have been tryin several means using gps devices buried inside the ransom money. the methodology is that the ransom money with the device buried inside is given to the hostage takers and they release the hostage. then we use the device, which we communicate with using gsm signals, to track them. it worked for a while but later the would collect the money, search it for any devices and clear it and deatroy it.

we are looking for a system that could be embedded in the currency without contortion and could be tracked remotely. in our research. we found that RFID technology could be used and by that i mean passive tags, but their read range is too small. so right now i am looking for a way to use technology to extand that range. it could be a hybridization of one or more of GPS, RFID, RADAR, or even GSM etc so that we could encode the passive tag in notes and track them remotely

i need responses from communication experts, system scientists, security professionals, researches in the above fields.