Do you use a Butter Bell?
I leave 1/2 stick (real) butter in dish on the counter at home and it's fine, but we're living on the road for a while and found mold in unrefrigerated butter (heat, humidity?) so looked into getting a Butter Bell.
I know butter has has to be softened enough to press tightly in the Bell. I heard a guy telling how much he likes his, but other opinions are welcomed. DH hates hard butter at the table.