I would go to a home store and ask them what product to use for glueing pavers on top of each other. I was watching yard chashers on DYI and they were putting the top pieces of stone on a wall and used something in a caulking gun under each stone to keep it in place. Another thought is using a piece of stone from a stone yard that would be the right demension for your base it would certainly be stable. Love your statue it will look very nice in your garden.
