That’s the worst. Happened to me a couple years ago and had to dig out like half my yard by hand to find the leak.
I seem to attract this issue. In order of occurrence:
1. Needing to replace the 8' deep line due to a sudden leak right as you're about to sell the house to move across the country. Then finding out the main line from the street to the meter is an almost 100 year old lead pipe when you get the section from the meter at the curb to the house replaced.
2. Coming home from a week with family at Christmas to find water running out of your house under the garage door. I don't really understand why anyone thinks running water lines un-insulated under a slab foundation is a good idea. We got lucky in that the water only crossed the garage as it headed out of the house, and I was able to re-route the pipe through the walls rather than dig through the foundation.
3. Helped a friend's parents replace one in Texas that a tree decided to grow through. At least there the lines are only a couple feet down.
4. Selling the next house to move across the country discovered the 6+" thick back cement patio was not original when the sprinkler system (important in Texas, it's even on the disclosure forms) decided to blow a leak 5' under it. A previous person didn't use sufficiently durable plugs when they capped off the old sprinkler and put a slab over it. The only way that didn't involve going through the slab was to crawl under a low bay window, dig through the 18" square between a bush, the house, a sidewalk, and the patio, then tunnel over 5' to the leak. Fortunately I have small friends who are up for an adventure, but digging the hole for her was less than fun.
Morals of this story:
1. Better outside than inside.
2. Don't let your water lines know I'm in town.