Except as provided in Section 20-25, it is unlawful to use any basket trap other than a basket trap constructed of wood or plastic slats. A legal trap must have an unobstructed opening or openings in the rear end of the trap not less than 1 1/2 inches square. It is unlawful to use a hoop net of mesh less than 1 inch bar measurement, or attached wings and leads of a material smaller than number 9 twine.