I think you have an answer. Search for a utility locating service.
But this is such a great PSA, because so many don’t understand how 811 works. They think that 811 will locate everything for free. They will not. They usually reach out to the utility companies themselves, who only mark what they own (they do often use contractors, and it’s often the same one do multiple utilities). They will not mark the private lines that go on your property. Water and sewer lines are usually customer owned after the curb. Oftentimes gas and buried electric and communications as well.
By all means, call. Where theirs end is a great clue as to where your lines begin, and you might never know what might be running through some decades old easement. But just because you are clear doesn’t mean there is nothing there. And if it is damaged, it’s on you to fix if you own it.
They will not mark the private lines that go on your property. Water and sewer lines are usually customer owned after the curb. Oftentimes gas and buried electric and communications as well.
And to expand on this and give more examples of private utilities just so people have an idea of what is around their house: landscape lighting, sprinkler systems, invisible dog fences, power/gas/water lines ran to a detached garage/shop/shed/pool/garden/greenhouse from the house, driveway alarms/bells, and motorized gates. If you live out in the country and you have a propane tank for gas, a septic system, and a well for water… those will not get located for free by 811 either, those are also private utilities that will require you to hire a locator to do for you.
I buried drops for an ISP one summer long ago, so I have a tiny bit of experience with the locate process and burying lines.