This year its being adopted at Copa America. It has been used for some years at the Copa Libertadores, a few more years in Argentina, and in Brazil, where it was invented, it has been used since 2000... it was already used in a national competition in 2000, at Copa João Havelange. ALWAYS with success. Its just ridiculous when I see referees in the World Cup, Champions League, etc, having a hard time to make the players in the barrier stay in place during a foul... [ame="http://www.youtube.com/watch?v=XdPClipUGj8"]YouTube - Spuni - Demarcador de Barreiras‏[/ame]
Yes, it is pretty annoying to have the wall walking towards the ball, but it's even more annoying when referees let it go. If players come within 10-yards before the ball is in motion, repeat the free kick, even if you have to do it over and over (unless the attacking team scores from it). It's already difficult enough to score from a direct free kick. Referees should be given access to any reasonable resource to aid them in enforcing the rules. I'm not sure why the spray isn't used globally, but I support it. I thought that back when it started being tested in Brazil, it would be and instant success, but good things take long to be adopted by FIFA for some reason. I think once it becomes a standard in Europe, it will be done everywhere.
My belief on why it was not adopted: Referees already have all the tools they need to enforce the 10 yards. There are two cautions that cover it: Failure to Respect Distance (FRD) or Delay Restart (DR). So why don't refs use them? Simple, they get accused of "cheap" yellow cards when they do, add in the extra cries if that "cheap" card is a second yellow, or the yellow that pushes a player over an accumulation limit. So, FIFA saw (in my opinion), no reason to add a gadget to a supply list when the rules already included the tools needed. It's amazing the effect giving a card or two for FRD/DR has on players, they suddenly realize what 10 yards is. It's the howling in the media, from coaches, fans and players when that "cheap" card has a real effect. The spray now is getting more popular because it's a proverbial "line in the sand" that makes it obvious to all involved and that for some psychological reason, helps players get where they are already required to be.