This limerick is based on a common logic puzzle, which has already been parodied in the great web comic xkcd here: http://xkcd.com/1134/. The last line ends in the mother-of-all slant rhymes, but use your imagination and I think it works OK.
You can just take one thing in your boat:
A cabbage, a wolf, or a goat.
But goat wants the cabbage,
And wolf wants to ravage
The goat. What’s the best way to do ‘t?