Sunday, 2 June 2013
depending if it a male or female dog.
but for water there is no real barrier
(this page discusses if someone leaves their home on shabbat whether or not their absence affects the neighbours in the courtyard and if they are still needed to make the eruv. it is assumed that if they are visiting their daughter, they won't be returning. but if they are visiting their son, their daughter-in-law may not want them, and she will bark, so they will have to leave and return home during shabbat. the talmud quotes a saying "if a dog barks you can enter; if a female dog bark, leave"
Also on the page is a cistern that is shared between two courtyards, and devising a type of partition, while acknowledging that water intermingles and there is no real barrier)