A Good Fishing Spot!

Two Irish friends rented a boat and went fishing in a lake. The first day, they caught 30 fish. As they were preparing to go into shore, one man said to the other, "Let's mark this spot so we can come here again tomorrow." The next day, when they were driving to rent the boat, the same guy said, "Did you mark that spot?" His friend replied, "Yeah, I put a big 'X' on the bottom of the boat." The first one said, "That was dumb! What if we don't get the same boat today?"