Help with procedures

So I'm making a mod about some illegal stuff and im adding a cop function, I want it to check every tick if someone is holding something illegal and tell them to put it away before the cops start running towards you. This is supposed to happen with 10% chance, but due to me not being able to cap it to do it only once per maybe 10 seconds it will spam it, and you basically have 10% chance per tick you hold it, so essentially 100% if you hold it for like 3 seconds. Anyone know how to cap it?

Summary: I'm not sure how to cap how many times a procedure runs every X amount of ticks/seconds 

Thanks in advanced