My pond is about a year old, I have pulled any young cat tails I have found growing around it. Earlier this summer, I noticed one pop up in a wet area on the other side of my barn, approximately 70 ft away. I decided to watch it's growth and progression since it was a good distance from the pond. The original growth got to full size, but had not grown a seed head yet. As of 2 weeks ago, there were 6 other new growths that shot out from the original rhizome. At that point I decided enough was enough with the amount expansion it created and hadn't even sprouted a seed head yet, I pulled all those suckers up. As others have said, tight, early control or they will quickly get out of hand. Those smaller ones are way easier to pull too!

[Linked Image from lh6.ggpht.com]