And many heavy smokers will never be under the limit...

For most people it only stays in the blood for several hours, but there are some studies that show it in the blood for a matter of days for heavy smokers...

The best strategy in the future will just not give them a reason to think that you're high. Cops will say anything (and even make shit up) if they think you're a stoner and they can nab you...

If I ever got pulled over and this became an issue I would DEMAND a field sobriety test. Hell, those are pretty easy to pass if you're not drunk!