A line of plain wire between the upper rails might be enough to stop another dog slipping through there, and perhaps just an electric tape 6” above the top may be enough to dissuade dogs thinking they can sail over. Wouldn’t change the vista much nor cost a fortune compared to changing it to a 5/6’ fence. Signs about the recent dog attack, cctv, electric fence in use, please keep your dog under close control, etc, may help awareness (or just upset people, it’s tricky).
Barbed wire makes owners careful. I HATE the stuff and would see it banned, but if there’s barbed strands I notice my friends putting Fido on the lead.