Restricting relationship field by author First site using Craft and impressed thus far.

I'm going to be allowing CP access for all users, and these users will have access to multiple channels. I want them to be able to relate their entries from different channels to each other, but only be able to select from their own entries within the relationship field.

I can't seem to find anywhere that allows this. I did a test with 2 separate users, and when I went to relate, I could see the other user's entries available for relationship in the entries relationship field. This won't be acceptable as each user should be in their own silo and only have the ability to relate their own entries.

Is there any way I can accomplish this that I'm missing? (edit: without custom field type)
Craft's permission system doesn't go down to the field level, which is what you're looking for.

You'd either have to replicate the functionality you're looking for on the front-end of the site, or develop a custom field type that took into account custom permissions for your users.