GC/MS is going to be the most accurate, it's the standard, but it's also very expensive (especially if you are wanting to procure a GC/MS machine yourself). You can screen for just about anything with a decent MS library. You'll want to do an extraction to clean up the sample (that should take care of your *sticky* concerns).
So many ways to do an extraction, might investigate solid phase extraction (SPE), it's typically used in industry for these kinds of things. You can buy SPE columns that are designed specifically for THC analysis (they use these in drug testing labs).
Alternatively, it might be a lot cheaper and easier to find an analytical lab to do the analysis for you.