Are you talking about some particular existing exhibit or probable planned exhibits?
Otters could be realistically incorporated into existing hoofstock paddock with water moat, by fencing the side of the paddock into the holding area of otters. I guess there might be a need of minor redevelopment of the lower part of perimeter fence and moat wall. It may be done by smooth concrete or plastic panels, or possibly a strand of electirfied wire on top of the fence. There is also a possibility of semi-circular metal overhang, like used in Maungatautari reserve in New Zealand against cats climbing in. And possibly, a filtration system could be installed in the moat. Otters would then have a run into the whole exhibit. Even if they don't stay in the moat but wander around the land area it should be interesting for visitors to see.
Zoo Basel has a new exhibit mixing short-clawed otters with indian rhinos. Otters climb on bathing rhinos etc.
If you want to restrict otters to part of the exhibit, it could be done by building a small sloping trench/moat/haha with a vertical wall maybe 1,2 m(?) high. Otters would then have access to water plus part of the land.
In smaller aviaries, I would add a separate holding area for otters outside the existing structure.
Also, I remember some very cool structure from some Japanese zoo, where small-clawed otters basically swim inside a thick plexiglass pipe going from the pool through the public area. The pipe is competely filled with water. Otters dive, swim into the public area, swim in this tank between visitors, then swim back to resurface.
There are also some zoos which build underpasses under public paths, so animals from one exhibit can visit another exhibit across the visitor path. Perhaps a thick metal pipe would be suitable for it (thick enough for a man to crawl through, just in case, or you may move the problem otter with a broom or water hose.).
Hope given you some ideas.
