Unless you dug the whole line up you probably wouldn't find the leak unless it was a very large leak which would bring the water to the surface, You would be better off just installing a new line.
Call a leak detection company. They will find your leak to within inches, and you will be able to dig down, repair the line where it is broken, and repair it.
There is no leak detector system made by Rainbird but there are ways to identify leaks in your system. One way is to turn off all water and see if your water meter is still running. Finding leaks can be difficult so you may want to contact a specialist.
you may have a septic system leak or a water main leak
they pollute the underground sources of potable water.
you should find out where the leak is, contact the customer to tell them what you have found and what you need to do.
you find out were the water is coming from after you fill it up with water.
You would have a leak in the coolant system somewhere and you need to have the system pressure checked.............
A leak like that can be difficult to find. If you live in an area that gets a decent winter, it likely is a spot where there was some water in the line when it froze, thus splitting the tubing. Regardless, the time spent looking for leak may be better spent just replacing the entire run of tubing.
pressurize the system. that'll make the leak leak faster and you should be able to find it easier.
I'm no expert, but here's an idea - turn off the filtration pump, and add some dye (maybe a lot?) to the water and follow the direction in which it flows - it should (eventually, I think) flow towards the leak.
You have a cooling system leak, you need to have the system pressurised to find the location of the leak.
You have to have a freon leak detector. Are you can put freon dye in the system and find a leak that way.
If you do not visibly see a coolant leak, have the cooling system pressure tested. If the leak is not obvious it could be internal.