“Forward cue” (slight forward pull on lead rope at halter). If not, train donkey by giving forward cue with lead rope and raising a crop in the other hand that is visible to the donkey. If no forward movement, smack donkey lightly on upper rear leg. If no response, pause, and repeat until donkey makes a forward movement with any leg. Reward donkey.
Repeat. Donkey will learn to move forward BEFORE crop makes contact with his body.