it's the same man who eats the fence
남자는 돌로 울타리를 지어요 should also be accepted
Only if the same man built it.
20/07/2021 it's accepted
Why is it 돌로 and not 돌으로?
its "-로" after vowels and ㄹ, and "-으로" after every other consonants except ㄹ.