Half Rests vs. Whole Rests

In teaching my daughter how to play the piano, the topic of the week was to introduce the half rest.  But how do you teach the difference between a half rest (which lasts two beats) and a whole rest (which usually lasts four)?  If you look at this graphic, they look very similar:

The only difference is that one rest is on top of a line, and the other is below a line.  But which is which?

Easy--I came up with this mnemonic:

"If you don't whole-d on, you'll half to rest."

See?  The whole rest is "holding" on the the line above it, and half rests just "have" to rest on the line below it.

There you have it.  Now you know the difference and you can teach others.