the old kippers tied to the exhaust used to work on cars at wedding (I stuck to confetti and chad). I often smell plastic bags when they have flown up and hit the exhaust of the car in front.

Modern cars are aerodynamically better in this respect so anything in the engine bay is a better target - where the smell can get up near the air intake. If you can find that - cat &/or dog pooh would linger.

If you have access to the inside - the world is your oyster - or sardine.

Personally I would go for the moderately annoying - and make it last for a very very very long time. Too much and they will solve the problem.

We would love to know the result but I guess this would be evidence - already is maybe.................. see ya in court.