In practice, how secure is a tenured position in the US? Coming from France, where any official academic position (i.e. associate professor or full professor, or equivalent positions at public research institutes) is a civil-servant one, and therefore automatically for life, I've been always intrigued by the "tenure" system in the US. 

While reading the Wikipedia article, I spotted the following paragraph:  


  While tenure protects the occupant of an academic position, it does not protect against the elimination of that position. For example, a university that is under financial stress may take the drastic step of eliminating or downsizing some departments.


Does this kind of elimination/downsizing occur a lot in practice? Is it possible to "cheat" and to pretend to cut a position in order to save money just to get rid of a tenured professor? Are there some laws stating that if a position is cut, then another equivalent one cannot be created right after?
I haven't seen any statistics on how many tenure professors have been fired, but most articles on the topic treat tenure as though it's a lifetime position (e.g., this Science article, "Tenure and the Future of the University"). Anecdotally, you will likely never meet someone who knows someone else who was fired from a tenure position; it simply doesn't happen.

Note, however, that the number of tenure track positions made available over the past decade been trending downward fairly significantly (see the same article, and simply do a google search on the topic to see more).