It may be best to try and find what others have done to solve the same situation for the same game - if it is widely considered to be a problem by other players, than there may be popular and well-tested house rules that already exist.
When dealing with a pre-made game like Settlers of Catan and not with a game of your own creation, your options are limited - you can either create house rules of some form, or simply accept that aspect of the game. It may be best to try and find what others have done to solve the same situation for the same game - if it is widely considered to be a problem by other players, than there may be popular and well-tested house rules that already exist. On the other hand, if there are not, it may be a sign that regular players do not consider it to be a major factor in play.