Someone could probably write a quick program to do a "setland" for each water province (wiping the poptype and sites), then erasing the neighbor lines for the province also. Maybe 0 the population also.
I think that removes all possible benefits? But you could also add insane levels of defenders also.
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per peer-pressure preoccupation
My maps, mods, and mullings can be found at
http://www.Dom3Minions.com