In terms of magic keep mostly the same (magic's risky enough as it is) but add the following:
Irresistable dispel: If an opponent casts with irresistable force you may attempt to dispel. The dispel will be succesful if more 6s are rolled than were in the irresistable cast. E.g. caster rolls 4,5,6,6,6 a succesful dispel would require 4 sixes. The opponent still suffers the miscast regardless of whether or not the spell is cast.