* Rabbit stool / a tiny tool (This plays on the small size of rabbit droppings and their potential use as a tool in some situations.)
* Rabbit stool / a woodland pool (This connects the rabbit to its natural habitat.)
* Rabbit stool / a forest rule (This is a playful way to connect the rabbit to the forest environment.)
Ultimately, the best rhyming pair depends on the context and the tone you're trying to achieve.