I'm not sure why, but it seems every time a possum is caught in my canine traps, the set goes dead. Move the set just a little and back in business. Now when I catch a canine, skunk, cats (including feral cats) and other critters, the set becomes a canine hot spot. I usually reset the same trap and make multiple catches, even after the animal is dispatched right in the set.

I also agree that the use of certain baits and lures will attract non-target critters. Set location can also reduce non-target catches. Out away from cover and red fox urine as the only attractor has reduced my non-target catch. There are some commercial lures that aren't as attractive to possums and such also.

Whenever I find a good location, I always make 2 sets fairly close together. That way (hopefully) if a possum finds the set first, there's still one open for the canine, and many times two canines are caught...on the same night.