Direct Burial Outdoor Cord, Weather Resistant Junction Boxes.

I'm aware of direct burial cable, but not in the form of an extension cord. And I'm not a big fan of it because it's too easy to put a shovel through it at some point in the future when you fail to remember it's there.. If I were doing that job, I'd be running PVC conduit underground, pulling wires with the proper rating, and terminating both ends according to code.

How often do you plan on using this "extension cord"? Why would it be a hazard?

Extension cords are not for permanent installation. A code-compliant branch circuit is the way to go.

extension cord is only good for 30 days of temperary use. if you want to meet code, you need to instal something permanent.

youd need to pipe and run THHN or direct bury UF cable.