Boundaries

How do you explain to your ASD child that there are boundaries he needs to respect?  I feel like a broken record, repeating myself on a daily basis, but not getting through to Puppy.

This has being going on for sometime now, years really.  Puppy sees something he likes, picks it up, and now it's his.  The problem with this is that I may or may not notice he's taken something until I see him with it after the fact. Later may be an hour or three days or a week.  To him, he's had it for a while already and so it must be okay for him to have it or keep it, even figures no one needs it.

I find myself talking to him over and over about the same thing. I've expressed how he needs to stay out of my room and drawers.  I think it's gotten worse ever since he realized that I started to hide things from him.  He was bright enough to figure out searching and it opened up a new world.  He found access to items he may not have even known were in our home.

 He also collects loose change to be able to buy things he shouldn't have.  Why couldn't I have a kid who collects money to buy sodas or candy?  Nope, he wants wallets and more wallets.

So I'll probably have to talk to him again this coming week about one thing or another that he's picked up that isn't his.  I'm thinking I might have to start locking doors to the bedrooms to reduce his temptations.  If things don't get better, I don't know what to do.  I don't feel like taking his things will teach the lesson, but it might help him understand the anger coming from me when my personal items are taken without permission.  However, I need to teach him NOT to take items, and NOT to create anger.