Gusher Guard for Roof?
Often over doorways, we install a simple 90 degree folded 6 inch flashing. You can slide a piece of this under the shingle tabs, two or three courses above the drip edge, secure it with a few shingle nails. I like to install them in the shape of an inverted "V". You can also use a piece of gable end drip edge to do the same thing. look in the section of the store where the flashing and drip edges are displayed and you will see the pre-bent 90 degree stock.