urgent: Ultrasonic Ranging Module for robot localization

[a1_pulse]

Im working on a project which is (ultrasonic-RF local positioning system for mobile robot navigation).
the mobile robot  will send sonar signal to  3 fixed boundary beacons so that the mobile robot's position 'll be determined. and an RF signal will be used for the synchronization matter.

ive been searching the market for an ultrasonic trasducer and a proper ranging module.
of course, the most common with high performance is polaroid now "senscomp" electrostatic transducer but the driving module "6500 sonar ranging module " wont work as a receive unless it has trasmitted a pulse. and this is a big problem since the 3 beacons wont be tx they work as rx only.

i contacted them and advices me wither to design my own rx circuit or to use a (SSR) to stop the trasducer from trasmission.

im not sure what to do.

ps: did any one worked on it before? if so tell ur feedback plz.

Thanks in advance