Ooh also, keep a look out for prisoners with the Freedom need, they're the troublesome ones normally. They'll seek out contraband in order to tunnel out. If your contraband availability is high then your escape attempts are more likely.
Some more things you might want to do to lower your escape rates:
Shakedown- find contraband and searching toilets to reveal tunnels.
Solitary Punishment for those with high Freedom need to suppress them.
But the best way to stop inmates escaping is to make sure they're happy and have regular contact with their families.
Hope this is helpful