Pro Rege, Lege et Grege

This easily memorable phrase is the motto of Perth Academy in the original Perth in Scotland.  The noble sentiment is: "For the king, the law and the people."

The three nouns rex, lex and grex are all third declension nouns in the ablative singular, hence the e-endings.

Quo Peregrinatur Grex Pastor Secum

I found this phrase while reading about Walter M. Miller Jr.'s excellent science fiction novel A Canticle for Leibowitz on Wikipedia.  Incidentally, there are so many Latin phrases used in this novel that there is a separate entry in Wikipedia  List of Latin phrases in A Canticle for Leibowitz

It means in English: "Whither the flock may wander, let the shepherd [wander] with them."  The useful vocabulary is as follows:

quo   whither (where to)

grex, gregis (m)   flock, herd

pastor, -oris (m)   shepherd

The fact that the word pastor means shepherd explains why some protestant denominations use the word for their ministers.  By the same token grex is the ultimate root of the word congregation.