[Bob Scott]

Jose, when I was on a SAR team, we often had to go into an area after it had been compromised by locals. It the dog is trained on scent specific (trailing/tracking a known person after giving the dog a scent article) It's not a big problem with a good dog.
Most of our live find work was air scent without a scent article. In those cases, ALL people not connected to the dog teams should leave the area or the dog will alert on ANY person in the search grid.
I personelly have never heard of a dog working two different scents at the same time. That doesn't mean it can't be done. I've just never heard of it.
We considered live and cadaver as two different scents, with two different commands. If one command was given, we expected the dog to ignore the other scent. It wasn't a problem with good dogs and good handlers.
If given two different live scents, I suspect the dog will follow the first one it finds a track, but, never having done it, I'm just guessing.
I might add. Tracking, to me, means foot step to foot step. While a great foundation for the rest, I think most succesful dogs will trail, meaning it will use ALL available scent. Foot steps, scent on surrounding vegetation, and air scent. Foot step tracking, on it's own, is for competition only. JMHO!

 

[Bob Scott]

I think Patrick hit on something important. Is the dog going to be used on or off lead? If off lead, you need a good recall/refind because you would never be able to keep up with the dog. If on lead, you definately better be in shape to run a marathon. I have the RCMP video on mantracking. Those guys are always running when on a hot scent. When in the chase after a criminal, FST is WAY to slow. Their dogs use everything available to them.

 

[Bob Scott]

As to more scenarios, you need to keep records of time of day, temp, wind direction, length and age of the track, surface the track is on, how the individual dog works, etc. Also keep a record of your failures. These can be a big help in learning.
The same track layed in an open field will give the dog a totally different scent then one layed on a fresh mowed field. Dog use the scent of the disturbed ground as much as they use the scent of the human. ALL these subtle little changes need to be a part of your training program.