Just as you like it

The German government wants to reintroduce border controls for the G8 summit in Heiligendamm from 6th to 8th June. Germany signed the Schengen Agreement and introduced it in 1995. So how is it possible to simply opt out for a couple of days as it suits you? It seems the government is afraid of (radical) left wing protestors and attacks.

To be fair there were attacks in the past, just remember Genoa in 2001. But I doubt very strongly that one can put so called suspects under "Vorbeugehaft" (which I guess can be translated as a preventive arrest) and indeed reintrodce border controls for a week or so - then abandon them again and say, well, principally Schengen is a good idea, but sometimes we just need the Cold War back.