The DS3231 is my favorite chip for this kind of application. With the IC and a lithium battery, you now have a battery-backed clock that drifts only a few seconds per year.
I thought the DS3231 is specified as accurate to 2 parts per million, an order of magnitude better than the uncompensated arduino crystal, but that's a around a second a week, how do you get the figure of a few seconds per year?