Superglue works great to seal a small cut with good edges, Barkingdog, and the glue dries fast--in a matter of seconds to a couple minutes--so licking can be prevented. Once it's dry, it's inert. It's even used in surgery to close some incisions.
If this wound is on the top of the tail, though, it almost seems more like an infection in the gland there than a cut. If that's the case, it's possible to treat with antibiotics--and maybe even to have the gland removed eventually. Sure looks sore!
