Once your dog is able to search for all three odors then you can start setting some really fun puzzles for them.  Before introducing Anise and Clove, it is important that your dog understands the game.  Ask yourself, will your dog search for Birch in the following elements: indoors, outdoors, containers, vehicles, and buried.   Your dog does not need to be fast, just consistent and happy working.   If this is the case, introducing Anise and Clove will be dead simple.  

For my classes, I keep my Birch tins mixed with Anise and Clove tins in a pelican case.  From day one the dogs are getting exposed to all three scents.  As a result, I have never had any problems introducing dogs to these new odors. 

However, I do find that it is important to take several steps back in training.   You will need to start from scratch with the new odors (but you will likely be able to skip steps and progress quickly). 

I find that it is not usually necessary to have the dogs feed over Anise and Clove (like we did with Birch).  Rather I set up a really easy search with just one hot box (either a switch box or a plastic container).  When the dog shows interest in the hot box, mark and reward.  From there, you can progress them to simple interior searches using the switch box, shell game searches, and eventually have them start looking for the tin!