It's easy to add an inseam pocket to a garment.  The pocket is shaped like a teardrop with one straight side about 8" long.  The pocket drops below the end of the straight edge.  Sew one to each side of a seam (the same distance from the top (or hem) using a 1/4" - 3/8" seam allowance (press seam toward pocket).  Then sew the seam, pivoting at the top and bottom of the pocket to include it in the seam.  Press the pocket toward the front.