The hardest part is getting a signal on the oscilloscope. Once you have that signal, you are measuring the time between the trigger and the arrival of the pulse. If you lose the signal, the problem is usually the trigger.
Yurikov, A., Nourifard, N., Pervukhina, M., and Lebedev, M. (2019). Laboratory ultrasonic measurements: Shear transducers for compressional waves.The Leading Edge, 38(5):392–399