In the collar FAQ, I posted 2 photos, one showing the black double chest harness I've used to belay the dog(s):
http://www.mycorgi.com/forum/topics/some-info-about-collarsI just added an important update:
I tested this before a scary log crossing over a dangerous river. The log was about 7 ft. above the raging current. I wanted to make sure it would hold the dog in a vertical hang, like a rock climber's seat harness, on a short rope if he fell off the log.
It will NOT! I had it very tight on Al, lifted him slowly off the ground, and he slipped right out of it!
This was very surprising; that harness looked bombproof. This harness ties in at the back, just above the withers/shoulders.
Reasoning that stresses would be less if he was floating in the current, I belayed him on a long rope instead of a short rope. If you're just trying to make sure the dog doesn't wash downstream in a river, some of these harnesses can tie-in at the front (collarbone area).
Note that you could hurt your dog -- tweaking a shoulder or foreleg -- simply by doing this test. I took that risk. He slipped out unhurt.
Related: My sister witnessed a tragic dog fatality, a dog tied in a pickup truck bed on too long a leash; it fell off the tailgate and strangled.