Spider Monkey enrichment

I am now an animal keeper at the Peoria Zoo (formerly Glen Oak Zoo) in Peoria, IL.  I have been here for about 10 months now.  We have recently initiated enrichment schedules (before enrichment was up to whoever was working that day).  Now the head keeper makes a monthly schedule with appropriate amounts of enrichment days for each species.  Since I am working primarily with primates (spider monkeys, lemurs, mandrill, tamarin) we do some sort of enrichment each day.

A couple of days ago the enrichment was "mechanical".  After some debating I decided to fill a small plastic kiddie pool with water, and put ball pit balls (like the ball pits at McDonald's playgrounds...) on top of the water.  While I never saw any of the monkeys playing with the balls, there were several that had been moved out of the pool.

I have been thinking of variations for this idea for a few days now.  Some ideas include:

• Filling the pool with ICE and mixing balls and/or diet pieces in with the ice (good idea for really hot summer days)
• Using fewer balls (I used all of the balls we had, so it filled up the entire top of the pool) and mixing food pieces in
• Putting frisbies in the water
• Putting larger balls, or balls of varying sizes in the water