Plastic fences where rails are inserted into holes in hollow posts are effectively stiffened by inserting into the hollow post a stiffening device which grips the rails extending into the post, and which is stabilized against movement so as to prevent angular deflection of the rails with the posts in a plane orthogonal to the longitudinal axis of the post. The tracking device comprises a magnetic tracking device, an optical tracking device or a laser tracking device. Moreover, the storage node base can be in the contact hole and the sidewalls can extend away from the base and away from the substrate with portions of the sidewalls being within the contact hole and with portions of the sidewalls extending outside the contact hole beyond the interlayer insulating layer away from the substrate. Or, it can be solved by a process for preparing an imidazolidin-2,4-dione compound which comprises reacting a mixed solution of a urea compound, glyoxal, and a base at 20 to 300\xb0 C.