I had a trench dug today so I can run my power in ground. I went 39" deep and I'm going to put 6" of sand then 3" conduit and another 6" of sand. we accidently pulled the last ground rod. but there are still two of them. do I have to replace the 3rd one or is two sufficient? I believe they are 8' long. the other ? is near the pole at the road we ran into a huge rock that the back hoe couldn't remove. the top is flat but it's only 28" down. my neighbour saidto just put 1" styrofoam on the rock and run the conduit on top then put sand. is this ok?