Gryphon,

Having seen lots of hippo on land and in the water(also just meters away while in a canoe, which is actually kind of scary!), I'd say that it's not as easy as you might think. At least to shoot one in a "ethical" way. I shot a hippo on land last year, and sneaking up to one in daylight is at least as diffucult as sneaking up on any other African animal. Perhaps more, as hippo are so paranoid, and flee for water if they just think something isn't quite right. And a hippo caught on land with you in the way will definatly try to chomp on you while running for the water.