Hmm, there have been a few "barking in the car things as of late??"
By and large I tend to think most of the people having this issue have made the dog thing the car is just some kinda portable X-Pen?? So the dogs are free to act a fool in the car??
For me driving is serious business and being a "Car" guy being stopped by local LE is not an "unusal" occurrence.
Long before I got my first dog, I remember seeing a news report of a family being pulled over and one of their "non" aggressive Bull Dogs hopped out of the vehicle to see what was up and the cop shot him down, end of story. Bottomline for me dogs ought not to be acting like "fools" in vehicles!
So for me ,my dogs don't exist the vehicle without an explicit command to do so period! In the old days?? I think I just put them in the car ,open the door and if them hopped out uninvited, I'd scoop them up and back in you go "Rufus" ... figure it out!
It took a couple of times but they all got it .... works out fine! If I get stopped I don't need a bunch of "Bully" looking breeds making LE "more" nervous!
The side benefit of "training them that vehicle is not a play pen ... if I don't turn around and see them, I don't know they are there.
And as a side note the only comment I have ever gotten in regards to my dogs in the vehicle "if" I get stopped, by LE is "Nice Dogs!'
So that's how I did it "old School" works out just fine!
But there are other options timeline depends on you. You could "Flank the dog" and roll up on the issue from an unexpected direction?? Teach the "Place Command" :
Fearful, Anxious or Flat Crazy "The Place CommanD - Boxer Forum : Boxer Breed Dog Forums
Teach the "Place Command" it trains "Calming behaviour" in dogs?? You train that and the in car behaviours might just disappear?? You'd put the dog in the car and say "Place!"
Or you could try the squirt bottle thing?? I don't know I've heard it works for some issues but not my style.
I don't tend to use a lot of tools myself (SLL) guy but if I had this problem??? I'd go with a bigger hammer and use a "Pet Convincer!"
Or go to bike shop and get a bicycle air pump.
I have heard from others that the "PC" is a pretty big hammer??
A member on Boxerforum used it and she said her dog freaked out, it also stopped doing whatever it was it was doing?? But she felt bad.
I told her "OK" the PC made your point drop it and just try the "Ptsss" sound like you mean it! The report back was ... "Ptsss" from her works just fine ...her point was made with the "PC" stop the crap now! She no longer needs to use the "PC."
As always ask questions and welcome aboard!