A California appellate court recently held that officers violated the 4th Amendment to the United States Constitution where they entered an apartment against the consent of the legal occupant after they smelled a "distinct odor" of burnt marijuana and saw an individual inside putting a pipe to his lips. People v. Hua (2008) 158 Cal.App.4th 1027.
If you find yourself in this predicament, the word to the wise is:
"Just say no [to the cops]". And, as I always do, I will caution anyone who believes that their Constitutional rights are being violated that they can't hope to win a motion to suppress evidence in the field. While being clear about the fact that you are not waiving your Rights is important, nothing about that suggests that you should kick the officer in the shins (or even be impolite to him or her). One audible, intelligible "No Thanks" should suffice. Screaming "no!" repeatedly in anger and/or frustration promises to bring on more unpleasantness and possibly new and different criminal charges. Just submit to their color of authority and wait until your day in court to seek the remedy to which you are entitled.