I had some bad experiences early on (a rental car that was not returned for over a month was among the worst) which led me to become much more cautious with my equipment, and who I let be around my equipment, so the amount of theft that I experience is minimal these days (the rental car experience also led me to quit shooting solo sites and serendipitously focus on my current multi-model site for the past decade).
I never shoot in my own home, and I generally work with a crew, so there are many sets of eyes watching out besides mine. Additionally, I don't allow alcohol or drugs on my sets (although I was known to get hammered once or twice on all-day shoots during my drinking days, hehe), and I would turn away any model/performer obviously impaired (only had to do so twice out of hundreds of shoots).
I've only worked with a few models that I even suspected of doing serious drugs on their own time...perhaps it is the niche I am in, since I can say in all honesty that most of the girls I work with are pretty straight and nice decent people. Some have even become close personal friends, even if we rarely work together anymore (models careers are often short, although I know some girls that are still going strong making modeling/performing a career for 10+ years and counting).
In a former studio, my partner was shooting a car with several models when one of his cameras came up missing. I came out because he was hollering at the models and interrogating them. I told him to calm down, and for everyone to look around, and then I led him back to the offices for us to "search" there.
Miraculously, the camera turned up just minutes later, and the girls told us that the silly photographer must have left it in the back seat, because that is where they found it.
Of course, we were back in the office watching studio surveillance camera video of one of the girls pulling the camera out of her big purse and putting it on the back seat of the car...soooo busted!
I routinely warn girls to be careful with their wallets, valuables, and especially jewelry and clothing around other models, since they are notorious for taking other girls' stuff.
Photographers I've worked with (at least 20+) have almost all been incredibly trustworthy, returning stuff I didn't even know I left behind on a shoot. I also have the best PA's ever (some with me for several years).
ADG