An easy trick is to take a common riddle that's likely all over its training data, and change one little detail. For example:

A farmer with a wolf, a goat, and a cabbage must cross a river by boat. The boat can carry only the farmer and a single item. The wolf is vegetarian. If left unattended together, the wolf will eat the cabbage, but will not eat the goat. Unattended, the goat will eat the cabbage. How can they cross the river without anything being eaten?

o3 solves this correctly and produces a great table illustrating the solution to always keep the cabbage safe.