According to the New Statistical Account for Fortingal (1845, v10):
Caisteal coin a-bhacain- the Castle of the dog’s kennel.
This bacan, or stake to which the Fingalians tied their stag-hounds, and from which the castle is named, is a thin stone, about 2 and a half feet in height, resembling the letter q, with the small end set into the ground, up on a little green eminence.
It is known as Caisteal a’ Chonbhacain, from a remarkable stone in its vicinity, which was till recent times practically an idol.
-from ‘The Circular Forts of North Perthshire’ by W J Watson, in PSAS for 1912, p30.
ads.ahds.ac.uk/catalogue/adsdata/PSAS_2002/pdf/vol_047/47_030_060.pdf
Perhaps that’s just a less coy version of BigSweetie’s quote below.