DCJ001,
How do you hold the player to the bet that he stated when his bet is invalid, and unknown? The problem that we are trying to prevent is when a player bets the pot and the next player reacts. Players have only a few simple options when it is their turn to act; call a bet, fold, or raise. If they are initiating a bet or raise they may either announce how much they are betting or raising or, push their chips forward into the betting area. The only action they shouldn't take is betting the pot, that is why we are having this discussion.
Establishing a house rule in this situation is easy enough, that is why I suggested the minimum. I think players will learn quick enough and they won't make that mistake again.