According to the Mishnah (52b), a non-Jew has the ability to nullify his idols. The source for this is brought in the Gemarain the name of Rav Yosef, based on the passage in Sefer (7:25) that obligates us to destroy the graven images of foreign gods. Basing himself on the Rambam, the Tosfot Yom Tov explains that since the Torah emphasizes that graven images of their gods must be destroyed, we can conclude that only those idols that serve as gods are included, but if the non-Jew has rejected them as gods, they are permitted.
The Mishnah on today’s daf (=page) explains what must be done in order for the idol to be considered nullified as a god. The Mishnah requires that an ear or nose be cut off, or that the idol is disfigured in some other way, even if nothing is broken off of it. If, however, the non-Jew merely behaved towards the idol in an offensive manner – e.g. if he spit at it or urinated before it, it is still considered to be avodah zarah. If the non-Jew sold it or pawned it, we find a difference of opinion between Rabbi Yehudah ha-Nassi who permits it and the Hakhamim who believe that it remains forbidden.
A number of rishonim (Rashba and Ritva among others) point to an earlier Mishnah (44b), in which Rabban Gamlielstates clearly that urinating before an idol shows a level of degradation that would indicate that it is not considered a deity. They suggest, therefore, that our Mishnah is talking only about someone who urinated before the idol once, but if that was done on a regular basis it would be enough to nullify the idol. The Me’iri rejects this, since in that case the idol was originally built to be used in this manner, and it was common practice to do this. In our case, where the idol was originally set up as a deity, a single individual urinating before it will not remove its status as avodah zarah.