There definitely needs to be a relationship buildup before accomplishing fear tolerances. Simple tasks with guidance by him prior to pushing the horses limits with fearful tasks will limit stalling out.
Once the trust is built, using a tarp is excellent. But in usingthe tarp, you can't just leave it in the stall, and even with food coaxing, it wont work. Pressure and release is the key. Introduce the tarp, remove the tarp, and again after a brief break. Once you gain acceptance, then take it to the next step and delay removal. Little steps. Due to the horse stepping on it with one foot.. I would have built off of that, and also praised heavily, but not with food, as the horse will associate food with other goals later on. But that one is just me. Leaving a tarp with food on it may be a good technique, but if you observe the same repeatative pattern with a bite, run, a bite, run, the its time to change something as that's not working.
Dixon's Red Hot Ember