How to Stop Email Spoofing

Set up Domain Keys Identified Mail on your own domain. That will digitally sign legitimate outgoing from your domain. More and more email providers are rejecting or flagging spoofed email where legit email is identified with a Domain Key signature.

Your question says, "apart from SPF..." and that's what I answered. However, for others who might use this answer, SPF is another deterrent. It is easy to set up, but has some limitations that should be considered carefully. You probably want to start with a SOFTFAIL policy.