The thieves must have used bolt cutters or some similar tool on the valve stems as the ones I found on the ground were pinched off not cleanly cut.
I met with our security system provider today and discussed upgrading our system to include more perimeter coverage.
I'm thinking a complete perimeter 8 foot fence and a remote gate with swipe card access would be nice.
The pursestrings are not something I control but this incident has definitely aroused the ire of our corporate security folk. I don't think we will have much problem upgrading the facility.