DMARC is layered across (/is useless without) two other protocols (SPF, DKIM), both of which also require DNS records.. there's no way to DMARC with one record.. unless you're excluding those SPF and DKIM records in your count. You /could/ DMARC with two records: DMARC+SPF, or DMARK+DKIM but it's ill-advised - use all three. (Ignoring host hierarchy/cname delegation, you can have far more records)

Do they literally just need the DMARC record to exist though, or do they need it to actually say something? Do you need DKIM? I found that SPF is very easy but DKIM is a royal pain.