The thing about it is, you can't idiot proof anything--the idiots are too damn smart.
If you want to be non-confrontational about it, I'd say reverse that $500 plan--they all split it in two months--every time they f*ck up a screen, take fifty out. Sh!t, give them a thousand twice a year--you'll save a lot more than that fixing the problem.
Perhaps joke about how much you're going to have to dock their pay because they are ruining so many screens?
(You probably can't, legally, but it might wake them up as to YOUR plight)
Hope something works out for you Alan.
I've been lucky to be in a small enough shop where I really barely have to let anyone else touch my rollers.
Last few years have been wonderful...