Thanks for your ideas. I ended up using what I had on hand - steel wool and duct tape. The steel wool raises the height of the reservoir and the duct tape holds it in place. I know they like to gnaw through things but they don't have any place where they have leverage to do so. The steel wool makes the top a squishy landing with nothing to give them traction.
At night when I am on the patio I can usually hear "tap tap tap tap tap tap tap" when they are drinking the water. Last night I heard nothing. It will be interesting to see the pics from the trail cam later today.
Edited by mercury - 2/22/16 at 10:57am