Ultrasonic Range Meter

I have attached a document of the circuit explanation of my ultrasonic range meter. But now I want to know if Im going to insert with in series with my 1M ohm resistor for the feed back of the op-amp to tune it for perfect 100db if the pot is not going to cause a bit of inductance due to the high frequency. 

Can you please help me with some calibration features/tips I can added into my circuits

Thanks and regards 

WS SA

Circuit explanation of Ultrasonic Range Meter unit 

oscillation circuit to control the sending-out time of the ultrasonic pulse.

The time of the oscillation pulse can be calculated by the following formula. Actually, with the error of the parts, it is different from the calculation a little. 

Circuit explanation for Ultrasonic Range Meter

The ultrasonic signal which was received with the reception sensor is amplified by 1000 times(60dB) of voltage with the operational amplifier with two stages. It is 100 times at the first stage (40dB) and 10 times (20dB) at the next stage.