> The nearer to the surface you get, the more protection—armour—you need to withstand potential disturbances from shipping. Trenches are dug and cables buried in shallow waters coming up onto shore. At greater depths, though, areas such as the West European Basin, which is almost three miles from the surface, there’s no need for armour, as merchant shipping poses no threat at all to cables on the seabed
Fishing trawlers are more likely to cause damage: By far the most common problems, however—accounting for about 60 percent of cut cable incidents—are dropped anchors and fishing nets.
The cables are on sea charts so this can be avoided, but that won't stop deliberate saboteurs. The strategy for safeguarding undersea cables has been described as “security through obscurity.”
http://arstechnica.com/information-technology/2016/05/how-th...