I was incorporating some anti-spam measures and thought that this would be good too.

you know, in remote places third parties forge some email addresses hosted in your server, send those emails from remote servers, and when the recipient server rejects the email on any grounds, it comes to your own server as the return address.

I have researched some rules for this, but couldnt decide on how best to implement it safely.

Anyone have done this before or have any insight on the matter ?

Yes, would be very interested in this also. This has been happening more than normal lately.
In our situation, it seems to be just a few domains that this happens to. I suppose one way to (help) prevent it in the first place would be to deploy SPF records.

SPF records are not useful i reckon when the forged email mimics the original forged domain's (like yourdomain.com that is residing on your server) actual host address as return ?

Since when the message is not delivered, the recipient host returns the mail to the return address or the sending host as non-deliverable.

I guess what is needed would be to define a rule that will spot a foreign address (server) in helo and refuse it.