It will slowdown the spread of cattails, but I have them coming up through even tighter rocks than rip rap. Best plan of attack is to remove all new growth asap. As in as soon as you see it. Heavy duty landscape fabric under the rip rap would work wonders. I do a lot of that now. Puts me out of work for cattail removal, but in some places like rockfilled spillways and shallows that are exposed during drawdown it is really the right way to go. I laways have some cattails to remove.
