Have to run about 40 feet or so of coax wire to a receiving antenna in my
backyard

Several people in our area have used gasoline powered Sidewalk Edgers to dig
a thin trench as deep as it will go then pushed telephone lines down into
the trench with thin board. Just loaned our Edger to a friend and he did
this. I would not do that as I do not believe you can get deep enough.

Walt Conner