here and here. After seeing the ones at Delcastle, I had the suspicion that there had to be more of them around. Then, sure enough, Tom Gears pointed out another one in Canby Park, and Ken Shelin recalled seeing one years ago in the Concord Pike/Naamans Road vicinity.
Those finds proved that the troughs at Delcastle were not unique, which made me even more sure that there had to be more out there. Well, we've got another one. Like the others, this one is located nowhere near Delcastle -- it's found in the yard of a house on Smith's Bridge Road near Granogue, in Chateau Country, northeastern Christiana Hundred. The house itself only dates to 1957, so the current owner (thanks for sending the pics!!!) believes that the trough was purchased and placed by the previous owner.
Looking at the trough and comparing it to the others, it's obvious that it is almost identical. The shape, the stone, the font of the date all look very much like the Delcastle troughs. The date is different (1904), but fits in with the others. For the record, we now have 1902, 1903, 1904, 1905, 1908, and 1912. This new trough, however, does have one feature not exactly found on any of the others, and it can be seen in the picture of the other side, seen below.
On the reverse side of the trough are the overlapping letters M and S. If you'll recall, one of the Delcastle troughs had an M on it, but that one was more of a solid, typeface sort of letter, not the thin, handwritten look seen here. I find it hard to believe, though, that the appearance of another M is just a coincidence. The mystery deepens......
Here's yet another one, as mentioned below in the comments. This one is in Hockessin.