Just a small suggestion, If snorkelers are going from the dock or kayak why don't you make them use a dives flag.
In Florida all snorkelers and divers must have 1 dive flag per group that they tow to be seem by boat. This is even true for people who enter from the beach. The resorts/houses can give them to guests to be borrowed.
If we still owned Ecologic we would make every divemaster carry 1 per group as the boat captains do always see the divers surfacing