I've proposed this a while ago on ZooChat, and I'm not sure if the policy still stands at the zoo which did this/if Cincinnati can feasibly do so, but this would be a good way of not only providing "more home to roam" for the hippos, but also providing a good amount of enrichment for the hippos and their neighboring species.
I read on ZooChat that at San Antonio Zoo, their hippo and wild dog habitats are adjacent to one another, and sometimes they'd let the hippos graze at night in the wild dog yard when the dogs were inside. Is it possible to build a transfer chute was built into Painted Dog Valley, so during the summer/evening events, Bibi/Fiona/Tucker can graze in that adjacent habitat?
It seems like a short enough distance to build a sturdy transfer chute/gate system between habitats, and not only do the wild dogs get a scent of hippo, the hippos also get a scent of *wild dog*.