Stopping barcelona is simple.......cut out the xavi-messi-iniesta triangle. however, simple things are difficult to do in this sport but not impossible ofcourse.
Another thing is to make your chances count. Barcelona loves to attack all the time, which often leaves the two defenders and CDM vulnerable to counter attacks.
No wonder Valdes is very good at rushing out of his box to kick out a ball. Casillas, on the other hand is arguably the best shot stopper in the world, but he doesnt see 1v1 situations as a regular part of the game, which is where his weakness lies. Take the recent loss to zaragoza for example. Casillas rushed out to clear the ball and completely scuffed it, allowing the zaragoza player an easy goal.
Teams in La liga play good technical football through counters or momentarily holding on to possession, but their major downfall is lacking a clinical finish.
This is why I am worried of Manchester United. Counter attacks and wing play are their strong suits and with a player like chicharito, who is being praised by everyone as a clinical finisher........even pele says chicharito might be the new messi, then again pele refers to himself in the third person

....but in any case he is being praised by many so I will keep an eye out for him.
The second goal for Hercules in their win against Barcelona is the perfect example of a clinical finish. Nelson Valdez received a low cross from the right and hit a one time shot, which flew in the upper 90. All the life in Barca players had been taken out then.