When a veteran's ashes are scattered at sea, there is no grave to mark. Some families still want a stone with a name on it, a place on land to visit. The Department of Veterans Affairs offers one for exactly this situation.
The VA's National Cemetery Administration furnishes memorial headstones and markers for eligible deceased service members and veterans whose remains were buried at sea, donated to science, not recovered or identified, or cremated and scattered. These memorials begin with the words IN MEMORY OF on the first line, and they must be placed in a recognized cemetery.
Both cemetery pages mention memorial walls. Neither says, in so many words, whether it will place a new memorial for a veteran scattered at sea. Call the cemetery before you apply and ask.
Use VA Form 40-1330, Claim for Standard Government Headstone or Marker. Include a copy of the veteran's DD-214 or other discharge papers; the VA asks that you not send originals. If the memorial will be in a national cemetery, start with that cemetery's office. The VA headstones and markers page lists who may apply and how to submit.
The GPS coordinates from the ceremony can sit beside the stone's record in your family papers. See the GPS coordinates certificate.
This is general information, not legal advice. Confirm current rules with the cited source or an attorney.