Excitement in the car

If the dog gets over-excited in the car and it isn't simply due to territorial aggression then it could be because he associates the car with some particular action or result - for example if trips in the car often end with a walk in the park. The very fact of being cooped up in the car can increase that excitement and sense of anticipation. 

The owner may try to calm him down by petting him and so unwittingly rewards the dog for getting excited!  The motion of the car and sound of the engine may cause conflict and fear within the dog and this together with confinement and frustrated anticipation leads to an increase in excitement.

To treat this problem, the dog must be systematically de-sensitised to whatever is triggering the excitement in the first place.  So - praise and reward the dog as long as he remains calm, but totally ignore the excited behaviour.

If the dog gets excited because he knows the car journey will end at the park, don't give him the reward of the walk until he's calm. 

Keeping small dogs on the floor so they can't see through the car window might help to calm them down.