First of all you need to ascertain whether or not his actions are deliberate.

At my home club there are a couple of those who also can't count. In the first couple of holes they are corrected by the marker and no doubt if they were cheating, they get the message they are being watched.

If the person is a good mate of mine - I'd pull them aside and bring it to their attention.

If the problem doesn't rectify itself - as a last resort the marker shouldn't sign the card.