"BAIT YACHTS" like the bait cars cops use to catch car thefts. Load up a yacht with Marines or Seals--heavily armed. Put an old couple on deck..sail into their waters. when the pirates approach..well you get the idea..take no prisoners. Three or four of those yachts floating around the area should do the trick in a month or two.
NO witnesses to report back..or if they did they might think twice about approach yachts..as for tankers..arm the crews whit automatic weapons, flack vests and rocket launchers and have one guy on board who can train the rest how how to use them.