If I made something like this id design it as a vibratory plow blade minus the vibratory function which isn't really necessary for these shallow installs. You will find having the proper angle on the toe of the blade is all you need to achieve depth it will cause you're blade to pull in farther rather than climb up. As far as the wire coming up in the trench that is going to happen at every depth to a certain degree, as you are pulling the wire is trying to pull taught which will likely cause it to raise a bit, you can cure that by anticipating it and building your blade slightly deeper to compensate. You could also make what we call a plug plow, just a thin blade tooth with a shackle welded on the back where you connect a chain and round steel plug larger than the material you are installing, set your wire up at one end of the trench on a free spinning rack and zip it in, the plug essentially bores a path under ground and pulls the wire through right behind