During my OW checkout dive at Coast Guard Pier at Monetery Bay, most people didn't bother locking up their stuff. They just left stuff sitting out or in back of their trucks. I was a little paranoid and disconnected my computer whenever we left the BC/tank/reg unattended. I figured that if they were to steal my BC/tank/reg, that's a lot of weight to carry. However, the computer (the most expensive part) was just a quick disconnect. Also - when we were in the water diving, all of our stuff were in our SUV and the SUV was locked. I felt like I was the only one paranoid.
Unfortunately, it only takes one bad apple to ruin the day.
