This is a big deal in Minnesota. The cattails here are usually very thick. You look for a game trail, walk the edge, or plow through. Obviously 100 acres of cattails you gotta really want it to bust through that and it's really not very efficient. A smaller patch then it's worth it. If you can find some that are not too tall or thick next to food then you're in business. For some reason it seems in the dakotas they have more cattail sloughs that are manageable. Shorter in height and less thick.
There is a spot in MN I hunt with a cattail patch about 7 or 8 acres on a fenceline. I'll walk the edge first, and often see birds. After that I'll plow in a little bit at high percentage areas. Sometimes you get a shot, other times just a glimpse as the bird flies away through a screen of grass.