How do I protect myself agianst injury/liability when hiring someone to work on my house, if they are not bonded?

There is no absolute way to protect yourself. As a general rule you should only potentially be liable IF you were at fault in some way in causing the injury (which can include having a dangerous condition at your home, however, like if a roofer falls through a rotted roof, or you have dangerous electric that shocks a non-electrician contractor; or a divot or hole in your lawn that someone steps into and turns an ankle), so it's not the case that you are automatically liable if someone is injured on your property. That said, there is certainly potential for a valid case--or for being sued on an invalid one and having to respond to it. Insurance will help--you should make sure you have adequate liability coverage as part of homeowner's insurance and should ideally also have an umbrella policy. But the real way to protect yourself is to NOT hire a contractor who is not insured, licensed and bonded. He should have his own insurance (and be able to prove it to) to cover him in the event of injury or accident. Unlicensed, etc. contractors *always* put you at risk--not just of accident, but in case they damage your home: an unlicensed contractor is much less likely to be able to pay for any damage he does.