Hey fishmasters!

Foul is ANYTHING on the bottom that will attract fish around it.
It can be a rock not much bigger than a couple computer cases in the middle of a sand or  mud flat, or larger, the size of a 3 storey building or bigger, an area of sea grass, a reef, sunken ship...or land based, a rock out in the surf, or the rock ledge that you are fishing over
When ever we head out, we take a slightly different route to the last routes.. and watch the sounder or anything 'interesting' on the bottom and mark it as a 'possible' for future reference. Then on one of the prospecting days, usually change of season , will stop on these marks, have a closer look, do a drift over with a few lines.