http://www.maisiefantaisie.co.uk/citrus-fruit-wedding-cake.html

How was this made to be stable? I would be afraid that the fruit would shift around???

that is a cute cake.

I would use skewers to hold them together and in place.

Well, first of all, the tiers are not resting on the fruit itself. The cakes are on pillars. The fruit is arranged in front of the pillars to hide them.

Unless the wedding is on a boat, I don't think there'd be a problem with the fruit moving after it was placed. To be extra sure, I think I'd slice a tiny piece of peel off of each fruit to give it a flat surface.