Searching for glacial max era artifacts or items of more recent vintage; shipwrecks and the like? In any case, I would imagine finding evidence of pre-historic civilizations offshore would be akin to finding a needle in a haystack. Where would one even begin? And what would one look for? Underwater pyramids maybe???
As the ocean floor gas hydrates start to be tapped for domestic energy markets, I'm sure we'll see much more in the way of A) discoveries and B) legislation purported to protect future archaeological site discoveries (but actually aimed at preventing development).
The best places to start *may be* the submerged estuaries, iow, along the rivers.