New to this trade, have an issue with a return line.
Return line does not hold pressure, used the XLT30 but could not hear the leak.
Pool deck concrete is covered with 1/2" of RubberRock.
Anyone have suggestions of how to find the leak?

If you can get an inflatable plug in the line, keep moving it and testing until you pass the leak and hold pressure.

how much pressure are you losing and over how long a time? small leaks are tough to hear. a pound a minute is difficult to find as you have to be in the right spot at the right time to catch it. how much the Pressure drops and over how long is important to know. sometimes you can chase a ghost. how much water is the pool losing daily?

Thanks for you input.
Looses 15psi in 5 to 6 min.
Cannot keep pressure up in line, have to use constant water or air to keep pressure between 5 to 15 psi while using Big Foot.
Cannot get a sound due to the Rubber Rock.
Would a Hydro phone in the pool or down the returns work?

Unlikley that the rubber rock is the problem. If the fill around the pool is rock, gravel and free draining you will struggle to hear it. Hydrophone is good as is getting an inflatable plug in the line.
Look for the obvious first, craked deck, ground movement, cracked plant room floor.