Yea drink a weak beer or a lager shandy and keep a pack of lager on the back seat minus a few cans so when they pull you they go for the breath test instead,wash your hands and face and brush your teeth and give your clothes a spray of some cologne or deoderant the smellier the better before heading home,most people that get saliva tested are stinking of weed they forget that they cant smell it but everybody else can.
If they pull out the saliva test its because one of them has already rumbled you for stinking of weed which they will let you know about.
Smoke hash instead its easier to swallow if transporting in your car and does not stink you up as bad,dont drive like an idiot,never look at them twice,keep your car clean of tell tale signs are a few other things you can do.