$h(i)>h(i+1)$ and $h(i)>h(i-1)$, [*i.e.*]{} provided that it is a local maximum. Should the the RSOS constraint be violated, the trial is discarded and repeated. Every $2(L-1)/[1-2\delta v (1-L^{-1})]$ steps the wall retreats one unit and, simultaneously, the interface is moved downwards by two units wherever it lies above the wall [@Ahlers]. The difference between the wall and interface velocities, $\delta v$, acts as the control parameter: if $\delta v$ is negative, the interface eventually depins from the wall, while for $\delta v>0$ it remains pinned). It can be easily shown, using random walk arguments that for the chosen wall velocity the system seats at its critical point. By varying it, we have a control parameter. The possibility of computing analytically the critical point largely simplifies the numerical analysis, and makes of this an efficient discrete model.

The quantities monitored are $\langle \exp(h_w-h) \rangle$ and $h_w-h$. We have measured the exponents $\beta_n$ and $\theta_n$ for a system of $L=2^{20}$ sites. Our results lead to $\beta_n=0.325(5)$ and $\theta_n=0.215(5)$, in excellent agreement with those of model 1 (Figure (4)). Once more, assuming $\nu_\bot=1$, we get $z \approx 1.51$ in good agreement with the scaling laws. In addition, we have also measured the spreading 