I'm no electrician but just did a long run out to my (daughters) new barn I have been a slave to for a year now. I think the best way for that outdoor stuff is to run a separate ground back to the service panel. That way it's really grounded. That's how the electric shop recommended I ground the sub panel out in my barn and saved messing with grounding rods in shale country. You might want to ask them if it is applicable for your situation. Conduit, the plastic stuff is so dirt cheap you would be foolish not to use it. Down south in sandy soil is one thing but when you live in the rock belt / rust belt like we do it's nuts not to with all the frost action , shale and sharp rocks.
I found what I had said before about that deal not using any electricity. It's pretty vague as it was third party when I read it and the guy said he read it in Westernhorseman Magazine. They do this for cattle in Montana in remote places.
In short this is the process. Get a long thin tank. Take backhoe ( I might just try this with my nice new one myself)and dig a trench long as the tank 5' deep. You then take 12" pipe in a "U" shape and bury it . Then you cut holes in the tank for the pipe and the natural flow of up and down with the cold into the warmer water below keeps it open. You do have to put an box with insulation around the sides and have a cover to put down on very cold nights. Of course you see there is a lot left out like what sort of pipe how you connect it leak free and how high in the tank it terminates ect...... I suppose it's out there if you want to go looking for it deeply enough,probably in that magazine I referred to.
Here is another FWIW on horseys. Those black Rubbermaid tanks. Do get the screw in bottom heater if you can for two reasons. Everybody loves them but there is a bigger reason. They say those tanks won't split when they freeze, WRONG. They won't as long as you have the heater in place inside that plug at the bottom. Without that the ice gets into that tiny horizontal 1.5" tunnel with no where to go and it will split there. Ask me how I know this??? So if you use the floater type make sure to get a plug , 1.5" IIRC and screw it in from the inside to keep the water out of that tunnel or if necessary from the outside and fill the hollow center with silicone ect so it can't fill up.
Another trick to keep it open is plastic balls, the kind you get at Wallymart that kids play with. About 10 -12" across. Not much bigger as the wind will carry them away. Take the ball leave it floating. The horses will keep the ice open except when it's extremely cold by hitting with their noses. That is more of a shoulder months trick though. I tried everything but plastic welding to fix that leak too and those Rubberaid tanks won't fix completely once cracked. Not even 3M 5200 Marine sealant or windshield urethane would do it so don't let em crack. BTW they really don't crack normally as the ice does ride up as it's supposed to do except for that plug tunnel so I highly recommend them and they are fairly cheap/ strong.
One more FWIW. If your daughter (or you) is in the market for farm gear MASSEY has a discount deal for people who own a horse. Up to 28% off list price for tractors / implements over $5,000. That's how I just picked up my 2014 Massey 3617 ,loader and backhoe for $27K. Their interest rates aren't fantastic at 4.99% but my credit union was 3.2 and neither of you will ever live long enough to see rates like that ever again. The program has been going a year or so and you can look it up online. We got the full 28% Just sayin in case she (or you) get the "gottahaves".