Electrical – Can chain link fence rail be used as electrical conduit

300.5 also specs 4" of concrete allows 0" cover (other than the 4" concrete) if it's wide enough (6" sideways from the conduit each way.) I believe that "equivalent" would allow things like concrete pavers or bricks as well as poured-in-place concrete for in-trench conduit cover.

Not sure how you approached "pressure water" boring - I'd use a section of the conduit size you want to run, or larger, with a section of smaller pipe inside it to run the water in - waste-water and dirt comes out the space between the two pipes, and the larger outer pipe directs the "drilling" - but roots and stones will stop that method, and it's not good for corners.

For tools you only need once, remember rental. But sometimes rental costs as much as having someone come do it.

I can't imagine how you'd envision pouring concrete separate from the trench to be in any way easier or more effective than pouring it in the trench. I can only see that as a complication that makes everything more difficult. Backfill and compact level with the top of the conduit, shape the trench to be wide enough for how deep the conduit is buried, pour the concrete - nothing easier than that if you have to use concrete cover.

Contact your local building department, and ask them if this would require a permit, and if you can do the work yourself. That's the only way to know for sure, as different areas have different rules.

You'll likely have to pay a small fee for the permit, and have the work inspected at different stages of the job (or maybe only once it's done). Most areas let homeowners do the work, as long as it's inspected.

If you do unpermitted work in your home, and something does happen. Your insurance claim could be denied, and/or you could be held personally liable for injuries and damages to others and their property.