In lieu of "Whoever smelt it..." debates, the chin defense could be used.
Once the scent of a bumtrump had been smelt then a clenched fist was attached to the chin. The last person to complete this action was identified as the fart culprit.
Of course, normally the first person to perform the chin defense tended to be the person who had farted - well aware of what they had just done and keen to escape the blame - and the loser tended to be anyone who had a bunged up nose or was too absorbed in colouring in the countries of Europe to follow the chinning trend.
This practice also evolved into double chinning, where the second hand should be placed below the first. Ultimately one would look rather like a Pharoah with one of those chin ornaments on - perhaps in his ancient regality a Pharoah was recognised as being incapable of letting off. I'm not sure, we did the Ancient Greeks instead of the Egyptians.