Its one of those things, you have to see to know, the rest is all talk. You have to make the call, have the location work done, then its still up to you on how to work with and around existing utilities. Something like that, I prefer to do some hand work, get an idea of actual location, try to establish direction, and of course that can certainly change, as what should be, is not. Also consider when "prodding" around, don't use anything conductive, and or use common sense and employ safe methods, mistakes can be fatal. There is no doubt about working around buried power, its dangerous, there is liability and whats on paper or shown by markings may not be accurate at all, every experienced excavation outfit would likely say the same thing. Something like that should be at a proper depth and when it was backfilled, say with a foot of cover on the conduit or line, there should be caution tape placed, so you can locate as you work. The caution tape should extend and rise up to where the line surfaces at the building, pole or what have you, makes it so much easier when doing hand work or physically locating the line, to follow whats there without risking damage, it also helps to have an experience operator that knows how to work around these things, hogging dirt out of a clean, (no underground utilities)foundation hole is one thing, working around, pipe, power and similar is another LOL !