Here is an example of a rule that uses "no-loop":
rule "Even Number Rule"
dialect "java"
no-loop
when
n : Number( number !=0 && (number%2)==0 , value : number)
then
modify(n){setNumber(8)};
end
Long story short:
Long story: http://ilesteban.wordpress.com/2012/11/16/about-drools-and-infinite-execution-loops/
Hope it helps,