wvmarle:
I suddenly picture a little dog standing in a doorway wagging its tail...
LOL... well you could try to make the code so that it filters out inconclusive data... 
Maybe if one sensor lights up and the second one doesn't also within five seconds, discard your data and assume that nothing has happened. And place the two sensors on the bottom far enough apart that they can't be triggered simultaneously by a dog wagging its tail...