Frothing around nostrils

Question
I have two Boxers; a female 18 months old and a male who is 6 months old. My question is as follows:
Max being a puppy  (6 mo old) and learning new things and experiencing different surroundings, we took a trip from Oklahoma to Texas (about 7 hours with the regular puppy stops.  Max seemed very stressed out when we stopped at a "busy" place for a potty break, Like a truck stop. I quickly took him back to the car to calm him down as my trying to to calm him outside was not working. I noticed that he had started to "froth" (white foam) around his nostrils, it concerned me at the time and as he calmed down it went away. Now this evening I had introduced him to a swimming pool which he loved. He loves to stick his whole face under water(while blowing bubbles) He does this in his water bowl too. He played for a little while in the pool and then he was done. My husband came home and wanted to see him in the pool, so he carried him to the pool and placed him in it, Max was not crazy about being in the pool so my husband let him get out. While the my other dog was playing in the pool, Max stayed off to the side, but he got this real anxious look on his face and and you can see the anxiety in his actions and his nose starts frothing. Is this something I should be concerned about, maybe advise on how to handle the anxiety? Please advise, Candy

Answer
The frothing is most likely just a type of sweating, like the 'lather' that horses get when they're worked up.

As far as the anxiety goes, without knowing what exactly was making him anxious it's hard to comment, but overall you want to reward good (confident) behavior and ignore bad (shy, anxious) behavior.  If you can pinpoint a trigger for the anxiety, you can work to change his response - teach him that the trigger means Good Things are coming, by heavily treating (most dogs are highly food-motivated, so treats are the most efficient reinforcer) whenever the trigger is evident.  He might ignore the treats at first; that's OK, but as soon as he shifts his attention to you, jackpot! (lots of treats, praise, etc.) and remove the trigger.  Here are a couple of articles about this "bar is open" technique:

http://www.k9infocus.com/casestudy7.htm
http://www.pbrc.net/training_cc.html

Good luck!