For the puddle, I would recommend Clear Resin like Shermanfeak said. I use Envirotex and it is a Resin varnish that works like a charm. If you want to use the future, I would think you would need to maybe use some foil in the depression so it will not get absorbed by the cel-u-clay.
Also, how long have you allowed teh cel-u-clay to dry before adding the future? Depending on how thick you made it, I would think you should wait a solid 36-48 hours before adding the future.