Before revision:  We study the depinning transition between the two fronts in the model at p= 1. At the depinning point, on a line of length L, the variance of the width of red front increases as L^{\alphaf(t/L^z) where f a scaling function with \alpha\approx 1 and z=1.67} 0.1 .
After revision:  We study the depinning transition between the two fronts in the model at p= f(t/L^z) where f a scaling function with \alpha\approx 1 and z=1.67} 0.1 .