Yosef Karo

“ If one intended to claim ownership of the shofar, they have not fulfilled their obligation, as it is now an object of idol worship owned by a Jew. (There are those who are stringent and who regard even blowing a shofar [that is an object of idol worship] owned by an idol worshipper as fulfilling their obligation unless the shofar's status as an object of idol worship was nullified before the holiday (Mordechai) . ”

“ Having a non-Jew do these things is permissible, because that is a rabbinic prohibition on top of a rabbinic prohibition. (Meaning, the prohibition of telling a non-Jew to do an action [on a holiday] that is prohibited by the Torah is a rabbinically enacted prohibition to ensure resting [shevut] from telling non-Jews to do things, and when the action in question is itself a rabbinic prohibition, this is a rabbinic prohibition on top of a rabbinic prohibition [shevut d'shevut] ) and when there is a commandment to do, the rabbis made no such decree (see 307) . ”

“ If it is an emergency situation where there is no other shofar available, it is kosher when patched with native material and the majority is intact, even if the voice does not return to its original sound. ”