I think the last time I did this I put it below the frost level but not in conduit. It doesn’t matter now because I sold the house and it passed a really strict inspection. Watch out for pipes,trees and things which could be in your path.. and oh yes, be sure the electric is off at the panel before you dig just in case. Call 1-800 Dig Rite before you dig. It is free and you will be sure there is no utility stuff down there. Let us know what you decide to do.