The electrode should be chemically very stable (used in very acidic and corrosive medium) and presenting an overvoltage higher than that of oxygen production.
Why particularly PbO2 electrode? You may easily prepare a saturated calomel electrode for measure electrode potential. Preparation of SCE is more easier than PbO2. This link about preparation of SCE may be useful. http://www.asdlib.org/onlineArticles/ecourseware/Kelly_Potentiometry/PDF-15-Ref&AuxElec.pdf