The best way to discourage ICS in MP, is to play diety and raging hoards on a real small map. Most people that live on ICS will refuse to play these settings so it must be a hinderance. Raging hoards and a small map almost guarentee that an ICSer can not isolate himself from others and barbs and expand at will. The only truely effective way to beat ICS is to find them early and eliminate them before they get entrenched. The diety setting also makes it critical that they get HG. If they don't, further hinderance.