I always sprinkle chlorine powder all over the floor of the car. Yu can't smell it but if a dog sniffs it, it burns horribly in the nostrils. Enough to render the dogs nose useless for a few weeks. Get the powdered chlorine at pool and hot tub stores. I got the idea after sprinkling powdered chlorine on my garbage bags outside to prevent dogs from eating my garbage. It worked great!! Dogs can't go near the stuff and the more they try the more they yelp and yelp! Damn dogs I'm not cruel to animals but I am defensive to anyone or anything that threatens my freedom .including trained cop dogs.