Today I learned the phrase 会社帰りに, which means “on the way home from work.” What makes this a little more interesting than it would otherwise be is the way it is read– かいしゃがえりに. Note the がえり, where you might have expected かえり.
Changing the pronunciation of words in compounds is common enough that it has a name– rendaku. It is yet another one of those things which you can’t learn by learning a rule. You just have to get used to what sounds correct and what doesn’t.