Remove the metal roller from a wire cheese slicer*
Congratulations… you just made a multitasker!
Now, get a knife…
No, a really big knife.
Now cut the watermelon into 2 inch thick rounds.
Cut a notch in the rind of each round.
Slip in the iwre of the cheese cutter and rotate the round 360 degrees.
Remove the rind in one perfect piece.
Bask in the adoration of all you survey.
*This one will do: https://amzn.to/2ZZWZF6