It could be he's a little concerned. With all the cheating going on. After all didn't Satan and Billicheat coach together. I wouldn't want any spies checking my game plan out. It could be far fetched. Just a thought.
An article about the closesd practice on espn.com said Osaban Been Lyin and Bellichick did coach together before and that OBL had been accused of stealing signals when he was the Dolphin's coach. I also read another article that hinted they may be worried about OBL spying since coach Searles used to coach with him and might have the inside scoop. Paranoia? Maybe, but there seem to be an awful lot of clues. Spies or not, the more private your game plan is, the better, IMO.