The best place to put watermelons is on somebody else's place!!!
When I was pretty small and my folks were out of the cow business for a while, a guy rented some pasture land from us to plant some crops - one of which was watermelons. The mound preparation made that pasture rough as a cob. Years of disking and plowing and dragging, etc, and it's still likely your butt's gonna leave the seat when you ride out there.
Watermelons are also a little tricky, as I understand it. Fine line between too much and too little when it comes to both water and fertilizer. At least that's what I've gathered from the farmers market growers. We had a lady whose husband passed last year and she tried to finish what he had planted. Very little of it was salvagable in the end.