Odds of Getting In
It's all about skill set and the job market. The entry-level jobs are pretty much always available, to some extent at least. Turnover in those gigs is fairly high, so if you can read, talk, and walk, you've at least got a shot.
The more intense jobs require the skill sets we've already discussed. They're usually hiring too, but how much and for what positions depends on whether the government or wealthy people are currently in the mood to pay a lot of money to have things or people guarded.