Try using a net and an elastic band. Using a small rock, but the zoo on it, cover it with a net and secure the net to the rock with the elastic. This has worked for me.
Why can't you superglue them. The gel works well
I use reef plugs. Dry off the base of the zoo a little and place a drop of Krazy glue gel on the plug, sit a minute and back in the tank. Mine always open right up afterwards.
