Aniseed

Aniseed is a simple plant-derived natural flavoring. A small quantity of aniseed extract can be used by a thief to ruin any effort to have dogs track his scent, if bloodhounds (or similar) are used by pursuers. Dropping a vial of aniseed down at a suitable place (e.g., by the bank of a stream the thief crosses, by the base of a wall he traverses, even at a crossroads) will ensure that the dogs' sense of smell is utterly ruined for 1d4+1 hours if they reach the spot where the aniseed has been dropped. A saving throw vs. poison will enable a trained dog to evade the aniseed to some extent, but the sense of smell is still lost for 1d4+1 turns. A spell such as neutralize poison or slow poison cast on an affected dog will eliminate the effect but the dog will still have to pick up the trail further along, somehow, to continue tracking. The effect of aniseed on any other kind of trained tracking animal is up to the DM, but aniseed should have a detrimental effect on almost anything's sense of smell.