implementing no-slip wall

Hallo ,
i am almost new to LIGGGHTS , i am running a simulation of a box (3d) , i apply a velocity to the top lid
while keeping the initial velocities zero at the begining ,
i started understanding (flow2 example in LAMMPS directory ) ,
i have a question , why when i change the lattice factor , i get my particles penetrating the implemented wall !?
- how can i prevent the particles from penetration the walls and not being lost and also avoid my whole domain to be scaled during simulation (since i use s as boundary condition ?!
- is it possible to have two lattice factors for one whole simulation , since i want walls as 111 planes and the flow with 36*36*36 cells . ?
thankx