Odds of Hanging On
The folks sticking around in this job are the ones who are obsessed with safety. It takes a superhuman level of attention to detail to see trouble coming a mile away and then head it off into a ditch. Don't be a problem solver. Make sure the problems are beaten long before they're worth the name.
It also helps if you're really into helping the environment and don't mind getting your hands dirty. Without commitment to the cause, it's unlikely you'll want to stick around.
A strong stomach or a bad sense of smell won't hurt, either.