This year I used Dr. Earth Life (there are various Dr. Earth mixtures with different designations) when moving trees to bonsai mixes.  It is organic and inoculates with mycorrhiza.  

I immediately had trouble with pests.  Initially I suspected ground squirrels due to previous incidents of digging.  Later I believe that a stray cat and possibly racoons were also likely.  I started with net baskets with a spike on the bottom that held about 3/4 tablespoon of fertilizer.  I would find them pulled out and opened and then left.  I tried moth balls and other methods to discourage the miserable vermin.  It was only partially successful - and I may have gained a cat and other critters.  

So, I went to Amazon and got some 2 inch net pots used for hydroponics.