If you're running 100 feet or more, I'd increase the size of your wire to #10 copper instead of #12 to account for line loss. (the smaller the number, the larger the wire). Bury a 1" conduit 18" deep minimum, 24" inches if you pass under a road way or drive way. Pull 3 single conductors instead of a cable, it will be an easier pull. Borrow a fish tape if you can. I stress running conduit over direct buriel UF cable because conduit is cheap once you've got an open ditch and offers a lot more protection from shovels, tree roots, settling, etc. Besides that, take a look at the price of a 250' coil of 12-2 or 10-2 UF lately. You can protect the entire circuit by installing a GFI in your breaker panel or simply install a GFI receptacle at the coop. If you're going to stay there for a while and you're running that far, take the time and do it right. I've been a licensed electrician for over 20 years and I'd be happy to talk you through it. As far as codes and NEC go, requirements for licensing and permits can vary from township to borough to city in PA; don't know about NJ. If this stuff is mostly beyond your abilities and you have to hire someone, at least consider renting the ditchwitch, digging the trench, glueing the conduit together and burying it. This is labor intesive but not highly technical work and will save you considerable money. Should you decide to go this route, consider any future needs for electric in that area as putting in a spare conduit while the ditch is open is usually money well spent.