I’m not certain that closing a particular site will have a real effect on providing substantial or even moderate protection from a single specific shark, especially in a location that is relatively compact as is Cocos. Here’s the thing about Tiger Sharks, Galeocerdo cuvier: they swim around.
Unless there is a specific reason for a shark or sharks to dwell in a specific location, (for example, near a sea lion rookery where large sharks come to prey on the pinnipeds, or as in St. Lucia where there is a small bay adjacent to a poultry processing plant where blood is consistently being dumped into the sea along with the rest of the industrial waste), then it may be a bit optimistic to presume that by avoiding that single site you will be able to prevent divers from encountering one particular animal.
Conversely, there was one particular cove very close to shore at Cocos that bore the monicker “Silverado”, where you could reasonably expect to see Silvertip Sharks, Carcharhinus albimarginatus, on any given day.