The first important fact I would need to know is where the parking lot is located.  Is it a parking spot located in the curtilage of your house?  If so, then there may an illegal search issue, since a very recent United State Supreme Court decision held that canine sniffs at a home are searches that require warrants under the Fourth Amendment.  If it is a parking lot located in a public area or a shared parking lot in an apartment complex, for example, then there is less of an expectation of privacy and more likely the canine sniff was not a search.
To the crux of your question–to be convicted of possession of illegal narcotics under California Health and Safety Code section 11377 the prosecution would need to prove beyond a reasonable doubt that your husband had both knowledge of the drugs in the car and knowledge of their nature as illegal narcotics.  Oftentimes, proof of this knowledge comes about from a person’s own statements or admissions.  Other times, the prosecution will use circumstantial evidence depending on where in the car the drugs were found.

Denying ownership of the vehicle is a common defense in these types of cases.  In any case, if your husband is being charged with a violation of HS section 11377, he should speak to an attorney immediately.  He or she would need to know these specific facts to properly advise your husband of his potential criminal liability.