Systems (100) and methods (1800) for making a marker housing. The methods comprise: forming a first housing portion from a flexible material so as to have a planar shape; and forming a second housing portion (700, 1200, 1500) from the flexible material so as to comprise a cavity (702, 1202) in which resonator and bias elements (104, 110) of the marker can be housed when the second housing portion is coupled to the first housing portion. The cavity is defined by two opposing short sidewalls (708, 712), two opposing elongate sidewalls (706, 710) and a bottom sidewall (704). The two opposing elongate sidewalls are stiffened such that crushing and bending thereof is made difficult. The stiffening is achieved by forming a plurality of first stiffener edge features (714) along an exterior surface of each of the two opposing elongate sidewalls which partially define the cavity of the second housing portion.