I've been making buttercream cakes for years and am very familiar with how to build a sound tiered cake, so that's not quite my question here :)
I've recently started working with fondant and delivered a wedding cake this morning. Before you get concerned, nothing bad happened and it looked lovely! However, due to using a cake stand and not using any topper (to cover a dowel hole) I had to assemble on site. With buttercream cakes I just stab the tines of forks firmly into the corrugations of the cake board, essentially making "handles" and I just lift the cake and set it where I want it. Lots of control. Then, I patch up the buttercream and finish out the borders.
With fondant, I don't quite have that fork trick available to me and even with spatulas and cake lifters and whatnot today I really struggled to feel as though I had a good grip on my tiers. They also had no bottom borders so I had to be incredibly careful of the fondant edges. Even though I brought along two friends to help it ended up being a really stressful delivery and the cake wasn't as perfect as I'd like (but that's graphic designer perfectionist me talking - nobody could even tell because I fixed the visual balance with the flowers). Even with overnight fridge storage and 20 minute transport in a plastic wrapped box the fondant still got a bit gummy because it is hot today, which made things even more tricky.
Given all of my story, when you're stacking fondant tiers what tools and tricks do you use to get the tiers exactly where you want them? What if you have to assemble on site?
I usually assemble on site if I have more than 2 tiers. I assemble the first two tiers at home. I use a cake lifter to place my tiers on top of each other or a large offset spatula http://www.wilton.com/store/site/product.cfm?id=F5E44F60-423B-522D-F605DA5FD1C1079F
All I ever used was my off-set spatula to gently lift one side of the tier just enough to get my fingers under the cakeboard. Usually I then bring ti to the edge of the table to lift it completely - of course depending on how big the tier is :) Try hard to center it before dropping it onto the other tier(s). I seldom had to adjust but if you do just push the cakeboard gently w/the spatula to center it Hope that helps:)