Pin it with tooth picks or metal rods, I use tooth picks, drill 1/16" hole ...stick tooth pick in a cordless drill and wrap 180 grit or less sandpaper around tooth pick and sand until it fits snug.
Tooth picks will swell tight in the water and are easy and cheap. Metal glue is usually needed not so with the picks.
Addressing the tail issue, quick fix/quick redo.. just dip the part of the tail you want thicker in heated clear plastisol.