It seems that the pirates do not attack in force. Why not just TRY to get every nation which is running cargo ships in the area to start randomly putting marines on them? Eventually the pirates will run into a very big problem for themselves. They won't know which ships are crewed with highly trained, well armed military and this should act as a deterrant at least.
For this to work I have to take the more violent side of things and say take no prisoners. Shoot them on sight and pursue them until they are dead
. Until they learn piracy = death then they will continue to do as they do. I'd have thought that in boarding a ship you would be at the tactical disadvantage so any casualties on the marines' side should be minimal.
Between the US and the UK we've got plenty of troops in backwater countries that we had no business getting into in the first place, so why not Somalia as well? At least our men would be doing something productive for a change and it would be good training for our collective marine infantries.
Really, and sadly, these pirates do deserve to get shot for what they put merchant sailors and their families through.