Stone (http://g603.net) glue?

Hi all. I'm a land (http://maplered.com) scaper and (http://maplered.com) I'm really out of my element when it comes to Stone (http://g603.net) work. My customer has a very heavy Granite (http://tanbrown.org) bench which came in three pieces, the seat and (http://maplered.com) two unattached supports. The supports are sitting on natural slate type Stone (http://g603.net) s which are pretty flat and (http://maplered.com) the whole thing is about as level as we can get it. The problem is that it tends to wiggle on the supports. Any suggestions as to how to fix this problem? Glue maybe? If so, what type?

Thanks