How to stop grease dripping on coals from catching flames?
Well these are not really techniques to prevent dripping fat from catching fire, as far as I know that is not easy to achieve, these are rather workarounds to minimize the damage.


Use some sort of water sprinkler system like a squirt bottle, sprinkler bottle or vaporizing or a squeeze bottle over the flames. If used moderately directly aimed at the flame area, it will reduce the flames without killing the fire.
Keep a box of ashes from previous fires around, when flames erupt sprinkle a little over the flame area. If used properly will have the same effect as the water above. It may be slightly less practical due to being harder to avoid inadvertently pouring ashes over the food, but its less likely to cool the fire.
Catch the fat before it hits the embers. If what you are grilling can effectively be cooked with indirect heat, then place a tray, box or any wide catching container to collect the fat before it hits the fire. Possibly filled with water to be easier to clean afterwards. It is what most electric and indoors grills use.