In order to bill someone for materials, you would have to be able to show that they received them, not simply that the materials fell out of the inventory tracker. Shorting the guys paycheck for arbitrary losses seems like a quick trip to a wage dispute complaint.
In order to claim that your employee insures you for losses of materials, you would have to be able to show that you have that written contract and that you pay a premium for this insurance, to claim on the policy.
The only thing I can think of as an inexpensive workable system is to have individual accounts per man at the supply house to draw out materials. Then you can look over the supply house invoices to see if the guy is doing service changes on the side with your material off the books.
You could pay the guy an incentive of $100 extra every week if he hits targets you set. But if you thought he was losing that $100 for the week, would you deduct it from his bonus or just fire the guy. If losses are noticeably a problem, it would be one guy taking 97% of what disappears and not 10 guys taking 10% each.
Losses occur statistically every year despite best efforts to mitigate. The names changes every year but the loss and payout rate remains persistent. Car fires, life insurance, big box theft, never stops and happens every year, at a consistently repeating rate.