NPC persistent attributes @red

I am currently creating a new Plugin that includes mount protection, because we had some griefers in the past days and i dont like searching for my horse every time and also i dont want to jail my animals to protect them, and also i dont want to prevent everyone from entering my property. So my current solution is saving a player ref in the npc name and it works well but i would like to have some persistent attributes i can add to npcs to make this somehow more elegant.

In the api reference i found nothing else i could use.