Welcome to ETO, samk9s!
The original poster (roger rabbit) disappeared into the ether without letting us know what he ended up using.
For my part, I still hold to my recommendation (overhead, adjusted cone shaped IR detection). I have built such a system that can detect something as small as 2yo child (and dogs, unfortunately
) from an overhead distance of >10' and a ground cone diameter of ≈4'. Drop the OH height and the ground cone size drops dramatically. Cone shape is
very adjustable.
As to the 1/100 sec timing, I don't know about that, but similar detectors at the start and finish will trigger alike (at the head, mid-body, whatever). The interval time accuracy will depend on the timer accuracy, not the triggering system. It's only one dog at a time, right?
Now, admittedly, if the trigger must
always be, for instance, only the dog's nose, then my system won't work. But on a "per-dog" triggering body point, I'm confident it would serve the purpose.