I have an idea but its quite difficult.
But if you can pull it off, i would pay for this.
- Npcs (police) can spawn at a players island, at random times (every couple hours or so).
- Police will chase/follow/run to the player, to search them (stop the players actions, and freeze them for like 5 seconds to do the *search*)
- IF the player has certain items in their inventory when searched, they will be fined/jailed.
(These items are usually just minecraft items with custom textures and renamed, so you would need to detect if the player is holding for example a Green-dye, with NBT 1 tag(s) and the name 'Weed'.
I know most of that is pretty easy to do if you are good at skript, apart from detecting an item with nbt data or a name if that works.
If you think this is something you'd be able to tackle give me a shout and we can discuss price, if its too difficult sorry;)