I was thinking that there should be a latch mechanism similar to this http://www.leevalley.com/hardware/page.aspx?c=3&p@033&cat=3,43586,43588 but instead of screwing on to the bottom of the leaf the latches would be seperate pieces. I would saw a slanted grove in the bottom of each leaf for the latch to catch on.
somthing like this
_________ ____________ ________ | |___________ Top of side table leaf ____///___| |__\\\________ Bottom side of Table has a saw slot running parralell to joining edges. /__________\ Latch Mechanism
There would be a possibility of getting lost when not in use, but extra ones could be latched on the leaves or ends that are in use.