I usually leave the car locked while at work, but at home it's sitting in the driveway with the windows down during daylight hours. At night I close it up but I'll leave it unlocked if I plan on going out later. When my 69 Camaro convertible was my daily driver I left it unlocked so people wouldn't try cutting the top to break in. Convertible tops are expensive to replace. And pet rocks are bred to jump through car windows!
Just don't leave anything in the car in plain sight and you should be fine. Oh yeah, leave your pet rock on the seat and see if it deters the thieves!