Returning belatedly to "thy rod and thy staff", and byb's inquiry as to the orignal hebrew words:
I e-mailed that question to a rabbi who runs a talmud sites. Promptly after close of the sabbath, Rav Lipman sent me the following reply:
there isn't a talmudic commentary, but I can tell you about a shevet and a mish'an, normally translated rod and staff (which is incorrect).
The Shevet was originally a pole used to hold a tribe's "emblem." (hence the word shevet also means tribe....) We don't know much from the Torah about these emblems; there is much Talmudic material about them. However, the pole itself was cut down to about 4 ft long and was used to keep a flock together by whacking strays with it. It was thin enough that it would not cause actual damage, but it certainly motivated sheep and goats to not stray.
The Mishan was similar to the staves used for defense described in the fight between Robin Hood and Little John; the mish'an was about six feet long and about four inches in diameter. It could scare off (or even kill) wolves and wild cats and other predators interested in the flock.
Hence the image in the Psalm is God as a shepherd with the appropriate equipment to keep the flock in line AND safe.
Neither the shevet nor the mish'an was used in war; even Little John resorted to a sword when going against the Nottingham deputies....
