My chavrusa and I have been learning Bava Metzia and have come to this section describing the loss as the vinyard, as opposed to the running animal.
We think this might provide an excuse in conflict with cases dealt with just a few pages back.
For example, if an elderly or dignified person did not want to erode his dignity to return a lost animal, but did want to protect a vinyard, can we say that he can shoo away a trampling animal to protect loss to a vinyard without becoming obligated to lead the animal toward its owner?
Since the Gemara rejected saying he could limit his leading of the animal to the area outside the city, it would seem that his devolved obligation to finish the task is pretty strong.
Similarly for the two rabbis, if the one shooing away the animal was only intending to maintain the cleanliness of the yeshiva in which they were learning, we don't seem to exempt the talmid from completing the task.
Perhaps the cases are not analogous.
Therefore we would like to ask:
If one wishes to protect their flower bed from a wandering dog, can they stop at shooing the dog away from the garden, and not catch the dog and find the owner? Or are they obligated to protect both the loss to the flower bed and of the animal?
As an extreme case, if one's obligation is only to the vinyard, would it be a solution to kill the animal to protect the vinyard?
Or in a simpler case, if there is a grazing land next to a vinyard, is it suitable to lead the trampling animal to the grazing land next to the vinyard, and let it loose there, without taking any particular steps to identify the animal's owner and ascertain if it was lost?
That is, if one has their intention only to protect the loss to the land of the vinyard, and not the loss of the animal...
Firstly, I don't see why, if a stray dog is wreaking havoc in a flower-bed, the owner of the latter deserves more assistance than the owner of the former. A person who is not a Zakein, would definitly be obligated both to save the flower-bed and to return the stray dog to its owner.
Neither will one have fulfilled one's obligation by letting the dog loose into an adjacent grazing-ground. You yourself write that one is obligated to finish the Mitzvah, so why should this case be different?
Finally, the Gemara on the previous page cites the case where Rabah informed Abaye that having thrown a clod of earth at some goats, he had become obligated to return them to their owner (even if he was otherwise Patur due to his dignified status). Rashi explains that this is because he caused the goats to move away.
In that case, the same ought to apply to someone who shoos an animal away (indeed, in the realm of Kinyanim, we find that one can acquire an animal in either of these two ways).
The only way the 'old man' would be able to protect the field or the garden without having to return the animal, would be by closing the gate or repairing the breach through which the animal entered.