Two men are out fishing and they are having great luck. They are catching so fast, they have to go back early.
"This is so great," says the first guy. "We should mark the spot so we can come here again."

"You're right," says the other guy who then dives over the side and paints a big X on the bottom of the boat.

They head back to shore and just as they're about to dock, the first guy looks at the second guy and says, "But what if we don't get the same boat next time?"