Pooling odor can create exceptionally difficult scent puzzles.  It can be hard to create pooling odor on purpose, but it is good to try, so that you and your dog has experienced this phenomenon, when you inevitably create a really difficult set up on accident.  Basically, pooling odor is a huge blob of odor that is far away from source.  This blob of odor is not directional,  it does not have a head or a tail and because if this it is very difficult for dogs to find source from that odor.  It is like an eddy on a river with a bunch of swirling water, that never really ends up flowing down stream.  
Pooling odor can occur below a hide, or to the side of a hide. It is easiest to set up a situation where the odor pools below a hide.  To do so, just set up an elevated hide with a bunch of stuff underneath for the odor to pool into.  When you are setting your hides, make sure to think about what will catch odor.  If you place a potted plant in the center of a scent cone, odor will pool around the plant because of the structure and the higher humidity.  Try to set up some pooling odor challenges for your dog to work through and give them time to figure them out. Sometimes, I find that Iona will need to leave and then retry to area from a different entry point to source the hides, so if your dog leaves the area without sourcing, see if they will come back.  
It is important to note that if your hide is inaccessible or if there is any converging odor, this set up will be WAY harder.  Stick to single scent cones at first.  
In this video, check out how these hides get more difficult as I add more opportunities for pooling odor.