Prompted by a recent incident in the waters off Gibraltar, between Royal Navy and police on one side and the Spanish Guardia Civil on the other, ThinkDefence has posted advertising and videos of a number of barrier systems. I’ve seen one of these deployed around aircraft carriers in San Diego. All are claimed to be effective against at least small boats, some against swimmers or larger vessels. Much of the interest in these systems goes back to attack on the USS Cole in Yeman.
Chuck Hill's CG Blog
Chuck Hill's CG Blog 
What killed the Cole was laziness and the old lack of “situational awareness.” Coming out of the Gulf all the ships took a collective sigh of relief and lowered their guards. I saw it aboard USS S. B. Roberts when we stopped to refuel in Djibouti. The ship put two under trained people with M14s on the outboard side, did not have crew served weapons on stand-by, and deployed no picket boat. They were a sitting duck. The general attitude was they were out of the “danger” zone and they could relax. Picket boats are but one part of the defense.
I had heard it was an ROE problem.
Most of these deployed barriers I have seen is use have been easily overcome by surface boats and offer no underwater protection. Another deterrent, but not impossible to overcome.