95:7 To make eiruvei techumin, one takes enough bread for two meals, or a side dish like onion or radish of sufficient quantity to eat with bread for two meals. An eiruv may not be made with salt or water. One goes to the place where he wants to deposit his eiruv and recites the bracha "al mitzvas eiruv," that G-d commanded us regarding the mitzvah of eiruv. (If one neglected to recite the bracha, the eiruv is nevertheless valid - Mishnah Brurah 415:14.) He then says, "By means of this eiruv, it will be permitted for me to travel 2,000 cubits from this place in each direction.'' (He must verbally express his intention for this to act as an eiruv even if he doesn't recite the actual text - MB 409:37.) He then returns to his home. One may leave an eiruv in one place for several Shabboses so long as he put it in a place where it will be protected from being lost or ruined.
95:8 One may send a messenger to deposit his eiruv. When the messenger places it down, he recites the bracha and says, ''By means of this eiruv, it will be permitted for (name of the one who sent him) to travel..." (If the one who sent him recites the text, "The bread that my messenger placed...," that also works - Bi'ur Halacha 409:8 s.v. vayomer.) The messenger must be an adult and mentally competent; one may not send a minor (nor a non-Jew, nor one who doesn't accept the law of eiruv - OC 409:8). Even if the messenger does not return to the one who sent him, he can be relied upon based on the presumption that an agent completes his appointed task.