Thanks very much Tim: yes, I have investigated alternative walls, both the split wall you suggest and a kind of two-layer set up with a smaller secondary wall behind the first. The problem, as mentioned in the article, is that gaps rapidly get filled (to un-sight the goalie) or, in the case of a secondary wall, it simply gets enlarged for the same purpose. Interesting too is the fact that scoring free kicks are becoming rarer, as evidenced in Brazil: wonder why??

One innovation was the very clever free kick taken by the USA (I think against Belgium), which had all of the characteristics of a "play" in American football and involved several linked components and not simply a direct shot. Maybe things are going more that way - more scope for modelling!

Ken