It's a hard job. At first, you may think that all it requires is discipline, being hard and strong, but being a prison guard is not as easy at it seems. Even though you have a lot of power over the prisoners, they are unpredictable and will likely cause many scenes that will bring you to risk. 

It's not a nice place to be in. People who work in penitentiaries have the same PTSD rates as war veterans. That should give you an idea of how rough this job is on your mental health. But if you trust your mental stability and are in need of some cash, I'd say go for it, but make sure to go to therapy if you feel the slightest negative effect on your mind. You wouldn't want to spend all your life with  PTSD if you can easily avoid it by taking care.

It's a risky job but not in the way people would normally imagine.