What you need is a list of property that you want to separate from community property. The final agreement can be signed together or signed in counterparts. Common practice is to sign before a notary to acknowledge that the signor is capable, 18 years or older, of sound mind, not under duress or coercion. Attorneys normally sign as witnesses. Typically each of you would have to retain an attorney. If one attorney drafts it, the other party must be given opportunity to seek independent counsel. Fees range from a few hundred dollars to a few thousand, depending on the complexity of the agreement.