I agree with Kathy... Besides stating what you want the people not to do, it's good to write a reason, as well. Letting them know the rocks hurt the fish explains why not to toss them into the pond, and makes people more willing to comply.
Welcome to the forum.
Oh, and hotels with ponds have been a great place for those of us who need to rehome extra-large fish. My ex took a number of large and quite pretty koi out to L'Hotel Soffitel in Houston, where they were happily received and are now living in LARGE quarters.