Most of the waters I fish they simply aren't known to be around, 2XL. (Doesn't mean they aren't there, just that they aren't known to be) Once in awhile I fish Winnebago or the Wolf river. They're somewhat common in the Wolf, but I fish it so seldom that I have yet to come across one.
I know they can be found over deep water like you mention. I've always wondered what they're doing there? They're ambush predators, not hunters. I wouldn't expect there to be much to ambush 1' down in 40' of water.