I have a few gazing balls secured to pedestals. Here's how I do it.
I purchase a "clay roll" which is kind of like fun Tac only more pliable and sticky.
Here's a link:
tiny.cc/nw27vz
you have to copy and paste the link
I take a long piece of the clay and roll it between my hands to form a long snake shape. I place the clay around the top perimeter of the pedestal and than carefully align the ball on top making sure I make good contact.
My gazing balls have survived a couple of hurricanes with no damage.