I'd love to see if I could get rights to a week or two in April and late September for fishing with my best friend. Don't know if that will be doable, of course. Depends on the personality of the new owner and how much of a break I'd give them on the price, I think.
Maybe offer the new owner free management advice (the value of which should be obvious) in exchange for some limited fishing privileges. You can discuss the "needs" of the pond after you and your buddy have performed your sampling!
