Check out this excellent article by Vancouver trainer Donna Hill.  She also has an excellent series of clicker training videos on YouTube for anyone looking for assistance with something in particular.

Unusual Signs of Stress in Dogs

By Donna Hill

What Unusual Signs of Stress have you Observed in Your Dogs?

Watch your dog for a week or so and observe him when he is in stressful situations. Or reflect back on situations when your do has been distressed or eustressed.

What specific behaviors that he doesn’t do in normal situations told you that he was under stress?
What level of stress does each indicate? (low, medium or high).
High ones are usually accompanied by other behaviors that indicate stress. Do you find this to be true for your dog?

Jessie clamps down on her bladder sphincter and can’t pee. She tries, but when stressed, nothing comes out. I see this when we arrive at new places with strange dogs such as a dog workshop. This a sing of high stress levels for her. By the first break, she has relaxed enough to pee normally.
When we first got her, she didn’t pee for 3 days. I thought she had a bladder infection and took her to the vet. Nope, she was severely stressed.
Another sign of stress for her is that she gulps-a big loud swallow. You can actually see the Adam’s apple moving and hear the gulp. It is usually done when I am too close and always accompanied by other signs of stress so for her, it’s a medium level stress sign.

A dog buddy of Jessie’s always sneezes multiples tie when she first greets Jessie. This is a eustress behavior for her as this is the only time it occurs (other than if she inhales something that needs to be sneezed out).