DS knows that when he leaves the table, that's it. No more food until the next meal (or designated snack). I can stop him getting down by helping myself to something on his plate, so he sits and guards the food he doesn't want for the next 10 minutes or so, but that's usually when he has finished his meal. My parents used this tactic with me and my sister and while I normally dismiss anything they did out of hand, this one isn't too bad.

I also get DS's food out last: firstly because of a "pack dominance" thing (if he's fed first he tells us what to do all night!) and also so he sees food on the table and comes of his own accord. But then, DH often finds computer games more important than food so I don't push DS to sit to the table - he often starts the meal a few minutes after the adults. But at the table he stays until finished.