Decide on the location and orientation of your trellis arbor; this arbor will be 8 feet by 12 feet when completed.
Dig a 3-foot deep hole with the post hole digger; have a shovel handy to help with the soil removal.
Measure 7 feet from this hole; dig another hole. These two holes will form one end of the arbor.
Measure 12 feet out and perpendicular to these holes; make two marks on the earth and dig 3-foot deep holes in these two spots. This will create a rectangular shape with the post locations.
Fill each of these four holes with 2 inches of gravel.
Place the 4 by 4 by 12-foot posts into the holes and brace them in place. Use the 2 by 4's to temporarily support the posts by nailing them diagonally onto the 4 by 4's and wedging them into the earth as bracing. Use a level to ensure that the posts are vertical.
Cement the posts into place. Use a hoe to mix the cement in a wheelbarrow according to the directions on the bag. Allow cement to dry overnight.
Boost the 8-foot long 4 by 4 up onto the vertical posts, on the side of the form where the posts are 7 feet apart.
Drill a 9-inch hole into the top of this horizontal member with a 7/16th inch drill bit.
Embed the lag bolt into this hole and tighten with a wrench.
Screw hooks into the vertical posts; these should be facing each other on the two end supporting forms. Place one at the top of a vertical post, one in the middle and one between these two hooks; you will now have three hooks on the upper half of the post. Repeat this hook pattern on all the posts.
Attach clothesline from hook to hook and tighten; the grapevine can now climb onto the clothesline and be pruned.