I would not use overhead for the cable, too likely to give problems
I would employ a firm to dig a trench and fit the rod in a proper pit clearly marked not one of those silly conduit boxes
you can hire machines to cut tarmac and concrete water cooled, but you should be able to find a groundworker to do it for you
if not cut into the house adjacent to the hillside
presumably the road is tarmaced and is the property of the house owner
the niceic do a good little book called snags and solutions earthing and bonding
they say that for longer runs of cable the impedance must not be so great as to cause the earth fault loop impedance to exceed the maximum value permitted by section 411
I have had the same problem with rustic properties and have used a contractor to cut a channel for me and lay a conduit in for the earth cable, this must then be covered by sand of a different colour to the soil and then warning tape or tiles ( so if some muppet digs it up he has a clue) dont used ferrous conduit use heavy guage pvc and install a pit making sure the soil level is below the top of the rod ( to prevent corrosion) and you will have to apply grease to the finished connections, the pit must be clearly marked safety electrical earth
with a bit of luck it may mount within a few feet of the house
however if it now a main road you are stuffed as you need permission and a street works cert to excavate and a cat and genny test before any cutting takes place outside so you dont chop the supply cables
do you not have any floors you cna lift to fit the rod under?
