When I had my cable laid 4 years ago (ntl days) I dug the front garden myself as I had seen how they did my neighbours and put spade in and pushed green conduit in about 1 inch lol.
I dug mine down a good 6-8 inches "ready" for when they got here (because I am nice like that
) Mind you they were so happy they did not have to dig and did help me recover with the earth and lay slabs back down so can’t complain. Heh I even found my BT line at 1 point that is only a couple of inches under.