Bava Batra 24 - Distance Regulations
If a young dove was found within fifty amot (100 feet) of a dovecote, it belongs to the owner of the dovecote; if farther than fifty amot - it belongs to the one who found it. Rabbi Yirmiyah asked, "What if one of its legs is within fifty amot but the other leg is outside of fifty?" - and for asking this question the Sages ejected Rabbi Yirmiyah from the house of study.
One must distance a permanent granary fifty amot from a city, and a temporary granary must be far enough from his neighbor's saplings or from his plowed field, so that the chaff that flies from the granary not cause them any damage.