Hilchos Shemittah v’Yoveil 4:29

If a non-Jew buys land in Israel and plants in it during shemittah, what grows is permitted. This is because the Sages only prohibited aftergrowth in order to prevent people from violating the law and non-Jews are not obligated in shemittah. Accordingly, there’s no reason to prohibit their aftergrowth.

Hilchos Shemittah v’Yoveil 4:30

When it comes to cities in Israel that are near the border, we appoint a watchman to keep people who crossed the border from taking the shemittah produce.