Rav shach does not usually state a halacha, but in his pamphlet of keeping damages away, he does actually bring the idea that most first authorities hold with the law of Tophot on page 22 of Bava Batra that the kind of damages that are brought in chapter 2 of Bava Batra are only considered to cause damage if on the other side of the border, there is already placed there something that could cause damage. And also, that if that is the case (that one has placed there something that can cause damage), then it can stay there even after the other person has placed his object there. And example would be like a tub used to soak linen that can cause vegetables on the other side of the border to absorb the noxious fumes. so, if that tub was already there, then even if the neighbor plants vegetables on the other side of the border, the tub can stay there [within three handbreaths of the border].