Hi @xDark013,
Here's my advice from another thread on contraband levels:
Yeah it's just one of those things. If you've got a prison with a lot of work spaces that the inmates can legitimately access, you're always going to have high contraband. There's no way to really stop it altogether unless you remove access to the contraband. Plenty of metal detectors, guards, regular shakedowns will keep it under wraps but it will always be high. I'd maybe recommend having a look at the Contraband menu and seeing what the common items are. Maybe they'll point out areas where your security is a little more lax.
The prison I'm currently playing has VERY high contraband levels but I'm also pretty secure and the inmates are all happy so there's no big drama 
Nat D11
Here's the thread