Measure 24 inches from the edge of the path on one side of the gate and mark it for a post hole. Repeat this on the other side of the path as well. Next, move through the gate and repeat the process to mark two more post holes. Try to keep these two post holes within 24 inches of the first two. Dig the holes 24 inches deep.
Place the 4-by-4 posts in the holes and pour the concrete around them. Place the level on the posts to be certain they are plumb. Be certain they are at least 8 feet above the ground. Let the concrete set overnight.
Measure the distance between the posts on the same side of the path. Measure the posts from center to center. Cut a 2-by-4 that length and secure it to the top of the posts.
Measure the distance between the posts on either side of the path. Cut two of the 120-inch 2-by-8s to the needed length to span the distance across the path. Drill countersink holes at an angle on the ends of the 2-by-8s. Secure them to the tops of the posts with the deck screws.
Measure the distance between the 2-by-8s from Step 4. Cut six pieces from the 2-by-4 lumber and space them evenly over the distance as cross members. Secure them with the deck screws.