I have a install to do that is 250 feet underground in the past i have just used a flat shovel just enough to cut the grass and some dirt under and lifted up the grass and stuck a CAT6 cable under it that has held up fine for many years. Only issue being a sore foot in the end due to hitting rocks. 
Since then i have a weed eater edger attachment, i'm thinking of trying it to dig a small trench with it. Sure you could rent a proper trencher but what is the fun in that.

Since then i have a weed eater edger attachment, i'm thinking of trying it to dig a small trench with it. Sure you could rent a proper trencher but what is the fun in that.