Walt and Jesse sure lucked out when it turned out that the guy who was hired to destroy their RV lab was also quite a scholar of Fourth Amendment jurisprudence. In season 3's "Sunset," Walt learned directly from the source that his brother-in-law Hank Scrader (Dean Norris) was tailing Jesse and looking for his RV lab, so Walt set out to have it destroyed. Clovis (Tom Kiesche) then directed Walt to Old Joe, who assured it could be compacted and shipped out without a trace in no time. However, Jesse, who was unaware that Hank was following him, showed up to intervene and got them both into a very bad jam. Hank showed up and was literally knocking at the door of the RV.
However, Old Joe stopped Hank from prying his way in by insisting that the RV was a private domicile and Hank would need a warrant to access it. He then sparred with Hank on issues of probable cause and displayed a thorough understanding of the nature of hot pursuit and evidentiary matters. Joe's quick thinking and apt advocacy bought Walt and Jesse enough time to form a new plan to get Hank away from the scene, and then Joe got back to the business of crushing the RV.
It's unclear exactly how Old Joe established such a broad knowledge of Constitutional law, but perhaps he was a civil rights attorney in a previous life because he was certainly skilled at slinging legalese when it mattered most.
